Parts Bulletin Imperial Series

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Optimas
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Torx® Pan Head, Slot Pan Head and Flat Head Machine Screws

Optimas designed the Parts Imperial Blog Series to provide detailed information about the fasteners you use and the ones you may need. Curated to help you find the right parts, these technical releases supply information on components’ specifications, applications and standards. This Imperial Series is comprised of five types of components: flat washers, hex cap screws, locknuts, machine screws and tapping screws. Once you have determined the parts suited for your application, Optimas can source them through manufacturing and distribution, ensuring you get the parts you need.

The Torx® slot, pan and flat head machine screws are designed to hold metal components together and have a specified minimum tensile strength of 60,000 psi. They are designed to be used with a mating machine screw nut, a standard hex nut of Grade 2 or higher strength, or a mating tapped thread. The threads are Class 2A thread fit and thread length is 1” minimum for diameters up to #5 included and 1-1/2” minimum for all sizes #6 and larger.

The Torx® drive allows installation and removal with a mating Torx® driver bit.* The Torx® recess provides excellent ability to apply sufficient torque to the fastener. Serviceability will require access to a Torx® driver bit.**

*Installation and removal of the Torx® slot pan head machine screw can be done with a slotted screwdriver. The added slot of a slot pan head allows serviceability with common tools.

** The countersunk head of the Torx® flat head machine screw requires an 80° included angle countersink.

Specification Resources

Dimensional and material requirements are controlled by ASME B18.6.3 and Torx® licensed standards. This type of fastener is generally available in sizes #4 through 1/2” diameter and length as shown in the tables listed below. Other lengths are possible.

 Torx® Pan Head Machine Screws

Top and side views of a Torx® pan head machine screw.
Torx® pan head machine screw

Torx® Pan Head Machine Screws

THREAD SIZE #4 #5 #6 #8 #10 1/4" 5/16" 3/8" 7/16" 1/2"
THREAD PITCH 40 UNC 48 UNF 40 UNC 44 UNF 32 UNC 40 UNF 32 UNC 36 UNF 24 UNC 32 UNF 20 UNC 28 UNF 18 UNC 24 UNF 16 UNC 24 UNF 14 UNC 20 UNF 13 UNC 20 UNF
HEAD DIAMETER .205/.219 .231/.245 .256/.270 .306/.322 .357/.373 .473/.492 .594/.615 .716/.740 .837/.863 .958/.987
HEAD HEIGHT .070/.080 .079/.089 .087/.097 .105/.115 .122/.133 .162/.175 .203/.218 .244/.261 .284/.305 .325/.348
THREAD LENGTH Fully threaded up to 1-1/8” included. Longer lengths are 1” min. thread length. Fully threaded up to 2” included. Longer lengths are 1-1/2” min. thread length.
DRIVER SIZE T10 T15 T20 T25 T30 T40 T45 T50 T55
1/8 - 1/2 (Lengths) –.02 (Length Tolerance) –.03 (Length Tolerance)
5/8 - 1 (Lengths) –.03 (Length Tolerance) –.03 (Length Tolerance)
1-1/8 - 2 (Lengths) –.06 (Length Tolerance)
2-1/4 - Over 6 (Lengths) –.09 (Length Tolerance)

*Common dimensions of Torx® pan head machine screws are given in inches.

 Torx® Slot Pan Head Machine Screws

Top and side views of a Torx® slot pan head machine screw
Torx® Slot Pan Head Machine Screw

Torx® Slot Pan Head Machine Screws

THREAD SIZE #4 #5 #6 #8 #10 1/4" 5/16" 3/8" 7/16" 1/2"
THREAD PITCH 40 UNC 48 UNF 40 UNC 44 UNF 32 UNC 40 UNF 32 UNC 36 UNF 24 UNC 32 UNF 20 UNC 28 UNF 18 UNC 24 UNF 16 UNC 24 UNF 14 UNC 20 UNF 13 UNC 20 UNF
HEAD DIAMETER .205/.219 .231/.245 .256/.270 .306/.322 .357/.373 .473/.492 .594/.615 .716/.740 .837/.863 .958/.987
HEAD HEIGHT .070/.080 .079/.089 .087/.097 .105/.115 .122/.133 .162/.175 .203/.218 .244/.261 .284/.305 .325/.348
SLOT WIDTH .035 min. .039 min. .045 min. .050 min. .064 min. .072 min. .081 min. .081 min. .091 min.
THREAD LENGTH Fully threaded up to 1-1/8” included. Longer lengths are 1” min. thread length. Fully threaded up to 2” included. Longer lengths are 1-1/2” min. thread length.
DRIVER SIZE T10 T15 T20 T25 T30 T40 T45 T50 T55
1/8 - 1/2 (Lengths) –.02 (Length Tolerance) –.03 (Length Tolerance)
5/8 - 1 (Lengths) –.03 (Length Tolerance) –.03 (Length Tolerance)
1-1/8 - 2 (Lengths) –.06 (Length Tolerance)
2-1/4 - Over 6 (Lengths) –.09 (Length Tolerance)

*Common dimensions of Torx® slot pan head machine screws are given in inches.

 Torx® Flat Head Machine Screws

Torx® Flat Head Machine Screw Parts Drawing
Torx® Flat Head Machine Screws Image

Torx® Flat Head Machine Screws

THREAD SIZE #4 #5 #6 #8 #10 1/4" 5/16" 3/8" 7/16" 1/2"
THREAD PITCH 40 UNC 48 UNF 40 UNC 44 UNF 32 UNC 40 UNF 32 UNC 36 UNF 24 UNC 32 UNF 20 UNC 28 UNF 18 UNC 24 UNF 16 UNC 24 UNF 14 UNC 20 UNF 13 UNC 20 UNF
HEAD DIAMETER .205/.219 .231/.245 .256/.270 .306/.322 .357/.373 .473/.492 .594/.615 .716/.740 .837/.863 .958/.987
HEAD HEIGHT .070/.080 .079/.089 .087/.097 .105/.115 .122/.133 .162/.175 .203/.218 .244/.261 .284/.305 .325/.348
ANGLE 80° / 82°
THREAD LENGTH Fully threaded up to 1-1/8” included. Longer lengths are 1” min. thread length. Fully threaded up to 2” included. Longer lengths are 1-1/2” min. thread length.
DRIVER SIZE T8 T10 T15 T20 T27 T40 T50
1/8 - 1/2 (Lengths) –.02 (Length Tolerance) –.03 (Length Tolerance)
5/8 - 1 (Lengths) –.03 (Length Tolerance) –.03 (Length Tolerance)
1-1/8 - 2 (Lengths) –.06 (Length Tolerance)
2-1/4 - Over 6 (Lengths) –.09 (Length Tolerance)

*Common dimensions of Torx® slot pan head machine screws are given in inches.

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