Westfield Fasteners Product Specification:

ASME B18.6.3 - UNF Slotted Countersunk Head Machine Screws

This product guide contains the specification for UNF thread Slotted Countersunk Head Machine Screws, a series of standard parts available from Westfield Fasteners. The basis of this specification is the ASME standard ASME B18.6.3.

Product Description

A countersunk head machine screw with a slot drive, designed to be tightened with a flat screwdriver. The countersunk head is typically used in conjunction with a countersunk hole providing a flush, snag free fit. Often used in consumer electronics and other small machinery where high torque fasteners are not needed.

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 UNF slotted countersunk machine screws, and describes the form, dimensions and tolerances, starting from the thread diameter of gauge size 0000, up to and including 3/4 inch.

The slot drive can have parallel or slightly tapered sides.

Dimensions & Tolerances of Slotted Countersunk Machine Screws according to ASME B18.6.3 (inches)

Nominal Diameter	TPI	These Lengths or Shorter are Undercut	Head Diameter, dk	Head Height, k	Slot Width, n	Slot Depth, T
0000	0.0210	160	-	0.040	0.035	0.011	0.008	0.004	0.007	0.003
000	0.0340	120	-	0.060	0.055	0.016	0.011	0.007	0.009	0.005
00	0.0470	90	-	0.087	0.080	0.028	0.017	0.010	0.014	0.009
0	0.0600	80	1/8	0.112	0.096	0.035	0.023	0.016	0.015	0.010
1	0.0730	72	1/8	0.137	0.120	0.043	0.026	0.019	0.019	0.012
2	0.0860	64	1/8	1.162	0.144	0.051	0.031	0.023	0.023	0.015
3	0.0990	56	1/8	0.187	0.167	0.059	0.035	0.027	0.027	0.014
4	0.1120	48	3/16	0.212	0.191	0.067	0.039	0.031	0.030	0.020
5	0.1250	44	3/16	0.237	0.215	0.075	0.043	0.035	0.034	0.022
6	0.1380	40	3/16	0.252	0.238	0.083	0.048	0.039	0.038	0.024
8	0.1640	36	1/4	0.3112	0.285	0.100	0.054	0.045	0.045	0.029
10	0.1900	32	5/16	0.362	0.333	0.116	0.060	0.050	0.053	0.034
12	0.2160	28	3/8	0.412	0.380	0.132	0.067	0.056	0.060	0.039
1/4	0.2500	28	7/16	0.477	0.442	0.153	0.075	0.064	0.070	0.046
5/16	0.3125	24	1/2	0.597	0.556	0.191	0.084	0.072	0.088	0.058
3/8	0.3750	24	9/16	0.717	0.670	0.230	0.094	0.081	0.106	0.070
7/16	0.4375	20	5/8	0.760	0.715	0.223	0.094	0.081	0.103	0.066
1/2	0.5000	20	3/4	0.815	0.765	0.223	0.106	0.091	0.103	0.065
9/16	0.5625	18	-	0.932	0.878	0.260	0.118	0.102	0.120	0.077
5/8	0.6250	18	-	1.050	0.990	0.298	0.133	0.116	0.137	0.088
3/4	0.7500	16	-	1.285	1.215	0.372	0.149	0.131	0.171	0.111

Nominal Diameter

TPI

These Lengths or Shorter are Undercut

Head Diameter, dk

Head Height, k

Slot Width, n

Slot Depth, T

0000

0.0210

160

0.040

0.035

0.011

0.008

0.004

0.007

0.003

000

0.0340

120

0.060

0.055

0.016

0.011

0.007

0.009

0.005

0.0470

0.087

0.080

0.028

0.017

0.010

0.014

0.009

0.0600

1/8

0.112

0.096

0.035

0.023

0.016

0.015

0.010

0.0730

1/8

0.137

0.120

0.043

0.026

0.019

0.012

0.0860

1/8

1.162

0.144

0.051

0.031

0.023

0.015

0.0990

1/8

0.187

0.167

0.059

0.035

0.027

0.014

0.1120

3/16

0.212

0.191

0.067

0.039

0.031

0.030

0.020

0.1250

3/16

0.237

0.215

0.075

0.043

0.035

0.034

0.022

0.1380

3/16

0.252

0.238

0.083

0.048

0.039

0.038

0.024

0.1640

1/4

0.3112

0.285

0.100

0.054

0.045

0.029

0.1900

5/16

0.362

0.333

0.116

0.060

0.050

0.053

0.034

0.2160

3/8

0.412

0.380

0.132

0.067

0.056

0.060

0.039

1/4

0.2500

7/16

0.477

0.442

0.153

0.075

0.064

0.070

0.046

5/16

0.3125

1/2

0.597

0.556

0.191

0.084

0.072

0.088

0.058

3/8

0.3750

9/16

0.717

0.670

0.230

0.094

0.081

0.106

0.070

7/16

0.4375

5/8

0.760

0.715

0.223

0.094

0.081

0.103

0.066

1/2

0.5000

3/4

0.815

0.765

0.223

0.106

0.091

0.103

0.065

9/16

0.5625

0.932

0.878

0.260

0.118

0.102

0.120

0.077

5/8

0.6250

1.050

0.990

0.298

0.133

0.116

0.137

0.088

3/4

0.7500

1.285

1.215

0.372

0.149

0.131

0.171

0.111

ASME B18.6.3 - UNF Slotted Countersunk Head Machine Screws

Figure 1: UNF Slotted Countersunk Head Machine Screw

Dimensions & Tolerances of Slotted Countersunk Machine Screws according to ASME B18.6.3 (inches)