Steel Door Inc.

American National Standard

Recommended Practice for Hardware Reinforcing on Standard Steel Doors and Frames

ANSI/SDI A250.6-2003 (R2009)
Revision of ANSI/SDI A250.6-1997


Table of Contents

  1. General
    1. Purpose
    2. Scope
    3. Reinforcing methods
  2. Metrication
  3. Reference documents
  4. Recommended reinforcing thickness
  5. Recommended application of hardware
    1. Mortised hardware
    2. Field drilling and tapping
    3. Thru-bolting
    4. Sheet metal screws
  6. Continuous hinges






It is the intention of this publication to furnish users and prospective users of standard steel doors and frames with practical information regarding accepted design methods for reinforcing and recommended practices for proper field preparation for builders’ hardware.


The information contained herein pertains to doors and frames manufactured in accordance with ANSI/SDI A250.8/SDI-100 “Recommended Specifications for Standard Steel Doors and Frames” published by the Steel Door Institute. It is not intended to reference architecturally specified or specialized situations beyond the scope of this document or documents herein.

Reinforcing methods

This standard recognizes as equal a variety of reinforcing methods produced by unique manufacturing processes. These processes include forming options (see figure 1) or integral gussets or fillets on lighter gauge members to achieve strength and performance equal to heavier gauge members.

1.3.1 — Where reinforcements require tapping for machine screw threads, an equivalent number of threads may be rendered in a lighter gauge part with a pierced and dimpled (“extruded”) hole as compared to a heavier gauge part manufactured with conventional processes. For example, equal thread depth can be achieved on a piece of 0.067" (1.7 mm) metal and on a flat plate of 0.123" (3.1 mm) metal (see figures 2 and 3). The extrusion process results in equal strength, equivalent number of threads and a lighter weight than the parent metal or equivalent flat reinforcing plate.


Metric (SI Units) are indicated in parenthesis following conventional linear measurements. These are “soft conversion” approximates based on HMMA 803 “Steel Tables.” Units without metric equivalents are indicated as (nm) (e.g. screws).

Reference documents

  1. ANSI/SDI A250.8/SDI-100 “Recommended Specifications for Standard Steel Doors and Frames”
  2. ANSI/SDI A250.4 “Test Procedure and Acceptance Criteria for Physical Endurance for Steel Doors, Frames, Frame Anchors and Hardware Reinforcings”
  3. Machinery's Handbook

Recommended reinforcing thickness

The Manufacturer, based on individual construction methods and tooling capabilities, shall reinforce their product to insure performance in accordance with ANSI/SDI A250.4. This reinforcing shall include (unless noted otherwise) reinforcing and tapped mounting holes for template hinges and ANSI defined locks as specified. Additional reinforcing for surface applied hardware shall be built into the door at the factory when specified.

As a guide to specification writers, table 1 shows the minimum thickness of steel to be used for hardware reinforcing as endorsed by ANSI/SDI A250.8.

Table 1 – Minimum hardware reinforcing thickness

Hardware Item Door Frame
inches mm MSG No.(6) inches mm MSG No.(6)
Mortise Hinge 1-3/8" [34.9 mm] Door(1) 0.093 2.3 12 0.093 2.3 12
Mortise Hinge 1-3/4" [44.5 mm] Door(1)(2) 0.123 3.1 10 0.123 3.1 10
Mortise Lock or Deadbolt(1) 0.067 1.7 14 0.067 1.7 14
Bored Lock or Deadbolt(1) 0.067 1.7 14 0.067 1.7 14
Flush Bolt Front(1) 0.067 1.7 14 0.067 1.7 14
Surface Bolt (3) 0.067 1.7 14 0.067 1.7 14
Surface Applied Closer(4) 0.067 1.7 14 0.067 1.7 14
Hold Open Arm(3) 0.067 1.7 14 0.067 1.7 14
Pull Plates and Bar(3) 0.053 1.3 16 0.053 1.3 16
Surface Exit Device(3) 0.067 1.7 14 0.067 1.7 14
Floor Checking Hinge 0.167 4.2 7 0.167 4.2 7
Pivot Hinge 0.167 4.2 7 0.167 4.2 7
Continuous Hinges(5) Not Required Not Required
Kick / Push Plate Not Required Not Required

NOTE: The minimum steel thickness for each specific gauge is derived from the published figures of Underwriters Laboratories, Inc.

(1) — Thinner steel may be employed as long as tapped holes used for mounting the hardware are extruded to produce an equivalent number of threads.

(2) — If reinforcing is angular or channel shaped, 0.093" (2.3 mm) is permitted.

(3) — When reinforcing is omitted, thru-bolting via the use of spacers or sex-bolts is required.

(4) — Reinforcement shall occur on both sides.

(5) — Refer to section 6.

(6) — MSG No. to be used for reference purposes only.

Recommended application of hardware

Mortised hardware

Standardized and ANSI defined preparations are made at the factory to allow installation of mortise hardware such as hinges and locks. Holes shall be made to precise diameters and accurately tapped to insure maximum thread engaugement and holding strength. Cutouts shall be pierced to surround the mortised hardware item to close tolerances on three or all four sides. The hardware shall be installed using only the proper screws as furnished with or specifically recommended for each device.

Note: The installer must exercise caution upon initial insertion of screws to prevent cross threading, especially with the smaller diameter screws.

Field drilling and tapping

Doors and frames shall be prepared by the installer in the field for surface applied hardware, such as surface closers or holders, track type concealed closers or holders, pulls, exit device cases, or vertical rod latches. In addition, some hardware such as anchor hinges, thrust pivots, pivot reinforced hinges or floor mounted pivots must be field prepared due to design variations or to provide adjustment that can only be provided at time of installation. The installer shall use a template provided with the device or the device itself to locate hole spacing.

5.2.1 — A suitably sized punch shall be used to locate the drilling for pilot holes to prevent drill creeping, off-center holes and improper screw alignment.

Important note: Use only the correct size drill for pilot holes, as recommended by “Machinery’s Handbook” (see table 4). Larger holes will decrease screw holding power causing the screw to be pulled from the reinforcing under normal stresses (see figures 4 and 5).

Tables 2 and 3 illustrate the effect of variances in pilot hole sizes on thread holding power.

5.2.2 — The installer shall assure that tapped holes have 75% of full thread (considered a normal condition). This percentage shall not fall below 65% to be considered adequate for proper hardware fastenings. Drills shall be positioned so the bit enters the reinforced area in perpendicular position as holes formed at angles will not permit proper seating of the screw head. After the proper pilot holes are drilled, proceed with the tapping operation. The tap shall match the thread size of the screws provided and the tap shall be held perpendicular to the surface.


Where reinforcing has not been specified or provided for other than mortised hardware, attachment shall be accomplished by thrubolting. The hardware manufacturer’s instruction sheets shall be closely followed for recommended procedures. Where thru-bolting is required on hollow metal doors, spacers or sex-bolts shall be used to prevent collapsing of face sheets as illustrated in figures 6 and 7.

Note: The most popular thru-bolting applications are door closers, exit devices, overhead holders, pulls and bar sets.

Sheet metal screws

Sheet metal screws are normally used to attach accessory hardware such as kickplates, mail slots, room numbers, identification signs, and in many instances, push or pull plates. These areas are not reinforced beyond the thickness of the face sheets. Properly sized holes and correct sheet metal screws as provided with the hardware item or as specified in the mounting instructions shall be used for hardware attachment.

5.4.1 — The best performance is achieved when the space between the threads is equal to or greater than the thickness of the face sheets.

Table 2 - #10-24 thread (nm)

Drill Size Drill Diameter % Full Thread
#23 0.154" 66%
#24 0.152" 70%
#25 0.149" 75%
#26 0.147" 79%
#27 0.144" 85%
“Machinery’s Handbook” recommendation in bold

Table 3 - #12-24 thread (nm)

Drill Size Drill Diameter % Full Thread
#15 0.180" 66%
#16 0.177" 70%
#17 0.173" 75%
“Machinery’s Handbook” recommendation in bold

Table 4 - Tap drills and clearance drills for machine screws with American National Thread form (nm)

Size of Screw No. of
Tap Drills Clearance Hole Drills
Close Fit Close Fit
0 .060 80 3/64 .0469 52 .0635 50 .0700
1 .073 64
48 .0760 46 .0810
2 .086 56
43 .0890 41 .0960
3 .099 48
37 .1040 35 .1100
4 .112 36*
32 .1160 30 .1285
5 .125 40
30 .1285 29 .1360
6 .138 32
27 .1440 25 .1495
8 .164 32
18 .1695 16 .1770
10 .190 24
9 .1960 7 .2010
12 .216 24
2 .2210 1 .2280
14 .242 20*
D .2460 F .2570
1/4 .250 20
F .2570 H .2660
5/16 .3125 18
P .3230 Q .3320
3/8 .375 16
W .3860 X .3970
7/16 .4375 14
29/64 .4531 15/32 4687
1/2 .500 13
33/64 .5156 17/32 .5312

Continuous hinges

6.1 — Standard preparation for continuous gear type or barrel type hinges shall not include any factory reinforcing, drilling and/or tapping in doors or frames. All mounting shall be prepared in the field by the hardware installer.

6.2 — For continuous hinges that require reinforcing (either for fasteners, door weight, door size or frequency of use situations) reinforcing shall be indicated at the time of order.

6.2.1 — Standard reinforcing shall be a 0.067" (1.7 mm) steel strip no less than 1-1/4" (31.7 mm) in width securely welded inside the hinge edge of doors and hinge jamb door rabbet of frames.

6.2.2 — Optional reinforcing shall be a 0.067" (1.7 mm) steel strip no less than 1-1/4" (31.7 mm) in width securely welded inside the hinge jamb door side face of frames.

6.3 — The hardware installer shall carefully follow the hinge manufacturer’s instructions for fastener preparations.


Appendix A


It has been the experience of the Steel Door Institute that most failures of hardware attachments have been caused by improper field installation rather than insufficient reinforcement. It is quite obvious that it is easier to tap an oversize pilot hole than to tap one of correct size necessary for maximum strength. Oversized holes will not ensure adequate product performance.

Manufacturing tolerances and dimensions may not always be consistent on machine and sheet metal screws when compared with different sources of supply.

The material used for the manufacture of screws is also a factor in the overall performance of the attachment. Stainless steel, for example, is a stronger fastener than aluminum or plain carbon steel. On installations where vibration or unusual frequency of operation is a factor, the use of thread locking inserts, liquids on threads, or binding heads should be considered.

Standard steel doors and top grade builders hardware are made to provide many years of service and are very compatible. The specification writer and construction superintendent must be aware, however, that proper installation methods must be considered on an equal basis with door and hardware construction requirements to achieve this compatibility on the job.

Appendix B


  • HMMA 830 "Hardware Selection for Hollow Metal Doors and Frames"
  • HMMA 840 "Guide Specification for Installation and Storage of Hollow Metal Doors and Frames"
  • ANSI/SDI A250.7 “Nomenclature for Standard Steel Doors and Frames”
  • SDI-117 “Manufacturing Tolerances for Standard Steel Doors and Frames”
  • SDI-122 “Installation and Troubleshooting Guide for Standard Steel Doors and Frames”

American National Standard

Approval of an American National Standard requires verification by ANSl that the requirements for due process, consensus, and other criteria for approval have been met by the standards developer.

Consensus is established when, in the judgement of the ANSl Board of Standards Review, substantial agreement has been reached by directly and materially affected interests. Substantial agreement means much more than a simple majority, but not necessarily unanimity. Consensus requires that all views and objections be considered, and that a concerted effort be made toward their resolution.

The use of American National Standards is completely voluntary; their existence does not in any respect preclude anyone, whether they have approved the standards or not, from manufacturing, marketing, purchasing, or using products, processes, or procedures not conforming to the standards.

The American National Standards Institute does not develop standards and will in no circumstances give any interpretation of any American National Standard. Moreover, no person shall have the right or authority to issue an interpretation of an American National Standard in the name of the American National Standards Institute. Requests for interpretations should be addressed to the secretariat or sponsor whose name appears on the title page of this standard.

Caution Notice: This American National Standard may be revised or withdrawn at any time. The procedures of the American National Standards Institute require that action be taken periodically to reaffirm, revise, or withdraw this standard. Purchasers of American National Standards may receive current information on all standards by calling or writing the American National Standards Institute.


(This Foreword is not part of American National Standard A250.3-2007)

The material contained in this document has been developed under the auspices of the Technical Committee of the Steel Door Institute.

The original standard was issued on July 28, 1980 and was revised in 1990 and 1998, and the 1998 edition was reaffirmed in 2004. The current edition is a revision of the 1998 document with the contents being updated to reflect changes and advances that have take place in the steel door and frame industry.

Suggestions for improvement gained in the use of this standard are welcome and should be sent to the Steel Door Institute, 30200 Detroit Road, Cleveland, OH 44145-1967.

The organizations that have approved this standard are as follows:

  • American Institute of Architects
  • Architectural Testing
  • Builders Hardware Manufacturers Association
  • Canadian Steel Door Manufacturers Association
  • Cedar Valley Associates
  • FM Approvals
  • Door and Hardware Institute
  • Door Control Services
  • HMMA/Division of NAAMM
  • Intertek Testing Services
  • Steel Door Institute
  • Therma-Tru
  • Underwriters Laboratories Inc.
  • Vetrotech / Saint Gobain
  • Wind Science & Engineering Research Center

The Accredited Standards Committee A250 TC-1 developed this standard and had the following personnel at the time of approval:

James Urban, Chairman
J. Jeffery Wherry, Secretary

Organization Represented Name of Representative
American Institute of Architects Joseph Berchenko
Architectural Testing Dan Johnson
Builders Hardware Manufacturers Association Michael Tierney
Canadian Steel Door Manufacturers Association Bud Bulley
Cedar Valley Associates Stan Horsfall
Ceco Door Products Tom Janicak
Curries Company Dave Dedic
Deansteel Claus Heide
Door and Hardware Institute Keith Pardoe
Door Components Tom Popow
Door Control Services Craig Ordmandy
FM Approvals Mark Tyrol
HMMA/Division of NAAMM Russell Tauscher
Intertek Testing Services Nancy Kokesh
Mesker Door, Inc. Mike Torres
MPI Tom Stone
Pioneer Industries, Inc. Kamal Sheikh
Republic Steve Gilliam
Security Metal Products Terry Simpson
Steel Door Institute J. J. Wherry
Ingersoll Rand Kurt Roeper
Therma-Tru Steve Jasperson
Underwriters Laboratories Inc. Matthew Schumann
Vetrotech / Saint Gobain Christian Mueller
Wind Science & Engineering Research Center Larry Tanner