Westfield Fasteners Product Specification:

ASME B18.6.3 - UNC Torx Pan Head Machine Screws

This product guide contains the specification for (UNC) Torx Pan 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 Pan Head Machine Screw (UNC) allows for these screws to be fitted with less chance of rounding when tightening. To be used in a pre-tapped hole or with a nut assembly.Typically found on consumer electronics and other small machinery where high torque fasteners are not necessary. Imperial Unifid Coarse thread version. Torx drive is a 6 lobed drive installed with a 6 lobed Torx screwdriver.

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 Pan Head Machine Screws, which 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.

technical drawing of UNC Torx Pan Head Machine Screws, ASME B18.6.3

Figure 1: Torx Pan Head Machine Screw (UNC)

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

Nominal Diameter		TPI	Recess Diameter, M	Drive Size, TX	Recess Penetration Gaging Depth, P		Fallaway
Nominal Diameter		TPI	Recess Diameter, M	Drive Size, TX	max	min	max
0	0.060	80	0.058	T5	0.020	0.015	0.009
1	0.0730	64	0.069	T6	0.030	0.025	0.014
2	0.0860	56	0.094	T8	0.035	0.030	0.019
3	0.0990	48	0.094	T8	0.038	0.033	0.019
4	0.1120	40	0.111	T10	0.045	0.035	0.022
5	0.1250	40	0.111	T10	0.055	0.045	0.022
6	0.1380	32	0.132	T15	0.055	0.045	0.026
7	0.1510	32	0.132	T15	0.060	0.050	0.026
8	0.1640	32	0.155	T20	0.070	0.055	0.031
10	0.1900	24	0.178	T25	0.085	0.070	0.036
12	0.2160	24	0.200	T27	0.085	0.070	0.040
1/4	0.2500	20	0.221	T30	0.100	0.085	0.044
5/16	0.3125	18	0.266	T40	0.120	0.105	0.047
3/8	0.3750	16	0.312	T45	0.145	0.130	0.055
7/16	0.4375	14	0.352	T45	0.159	0.144	0.062
1/2	0.5000	13	0.446	T50	0.180	0.165	0.078

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