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Westfield Fasteners Product Specification:

ASME B18.6.3 - UNC Torx Truss Head Machine Screws

This product guide contains the specification for UNC Torx Truss Head Machine Screws, standard parts available from Westfield Fasteners. The basis of this specification is the ASME standard ASME B18.6.3.

Product Description

Torx Truss Head Machine Screws (UNC) have a wide and shallow domed head, which can be used without the need of a washer. The head shape also gives a larger contact area with the surface, which means a snag free fitment and helps guard against tampering. For use either in a pre-tapped hole or with a nut assembly. Ideal for sheet metal projects and applications where there is minimal clearance, such as sliding supports in draws and cabinets. Imperial Unified Coarse thread version. Torx drive is a 6 lobed drive installed with a Torx screw driver.

Scope of the ASME Standard.

Unlike ISO standards, each ASME standard generally covers a range or family of product types. ASME B18.6.3 covers many machine screw types, including these UNC Torx Drive Truss Machine Screws, and decribes the form, dimensions and tolerances, starting from the diameter of gauge size 0 up to and including 3/4 inch. Figure 1 and table 1 below show dimensions and tolerances for the most likely seen sizes.

Figure 1: Torx Truss Head Machine Screw (UNC)

Table 1: Dimensions & Tolerances of UNC Torx Truss Head Machine Screws, according to ASME B18.6.3 (inches)

Nominal Diameter		TPI	Recess Diameter, M	Drive Size, TX	Recess Penetration Gaging Depth, P		Fallaway
					max	min	max
6	0.1380	32	0.111	T10	0.055	0.045	0.022
7	0.1510	32	0.132	T15	0.045	0.035	0.024
8	0.1640	32	0.132	T15	0.055	0.045	0.026
10	0.1900	24	0.155	T20	0.071	0.055	0.031
12	0.2160	24	0.178	T25	0.090	0.070	0.036
1/4	0.2500	20	0.200	T27	0.090	0.070	0.040
5/16	0.3125	18	0.266	T40	0.95	0.080	0.047
3/8	0.3750	16	0.312	T45	0.125	0.110	0.055
7/16	0.4750	14	0.312	T45	0.155	0.130	0.055
1/2	0.5000	13	0.352	T50	0.150	0.130	0.062
9/16	0.5250	12	0.446	T55	0.190	0.165	0.078
5/8	0.6250	11	0.446	T55	0.190	0.165	0.078
3/4	0.7500	10	0.529	T60	0.230	0.210	0.093

For verification of details and for further information please refer to the ASME standard document. E&OE