Westfield Fasteners Product Specification:

ASME B18.6.3 - UNF Slotted Fillister Head Machine Screws

This product guide contains the specification for UNF thread Slotted Fillister 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

UNF slotted fillister machine screws have a large cylindrical head, with a slightly convex top surface. These Fillister head screws are the preferred head type for counterbored holes and can also be used for protecting a surface by raising the level which the screwdriver is used to tighten the fixing.
A fillister head has similarities to a Pan head machine screw, but the fillister head machine screw has a greater side height, and the height to diameter ratio of the head is larger than a pan head.

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 fillister 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.

Table 1: Dimensions & Tolerances for UNF Slotted Fillister Machine Screws according to ASME B18.6.3 (inches)

Nominal Diameter	TPI	Head Diameter, dk	Head Side Height, H	Total Head Height, k	Slot Width, n	Slot Depth, t
max	min	max	min	max	min	max	min	max	min
0-80	0.0600	80	0.096	0.083	0.043	0.038	0.055	0.047	0.023	0.016	0.025	0.015
1-72	0.0730	72	0.118	0.104	0.053	0.045	0.066	0.058	0.026	0.019	0.031	0.020
2-64	0.0860	64	0.140	0.124	0.062	0.053	0.083	0.066	0.031	0.023	0.037	0.025
3-56	0.0990	56	0.161	0.145	0.070	0.061	0.095	0.077	0.035	0.027	0.043	0.030
4-48	0.1120	48	0.183	0.166	0.079	0.069	0.107	0.088	0.039	0.031	0.048	0.035
5-44	0.1250	44	0.205	0.187	0.088	0.078	0.120	0.100	0.043	0.035	0.054	0.040
6-40	0.1380	40	0.226	0.208	0.096	0.086	0.132	0.111	0.048	0.039	0.060	0.045
8-36	0.1640	36	0.270	0.250	0.113	0.102	0.156	0.133	0.054	0.045	0.071	0.054
10-32	0.1900	32	0.313	0.292	0.130	0.118	0.180	0.156	0.060	0.050	0.083	0.064
12-28	0.2160	28	0.357	0.334	0.148	0.134	0.205	0.178	0.067	0.056	0.094	0.074
1/4	0.2500	28	0.414	0.389	0.170	0.155	0.237	0.207	0.075	0.064	0.109	0.087
5/16	0.3125	24	0.518	0.490	0.211	0.194	0.295	0.262	0.084	0.072	0.137	0.110
3/8	0.3750	24	0.622	0.590	0.253	0.233	0.355	0.315	0.094	0.081	0.164	0.133
7/16	0.4375	20	0.625	0.589	0.265	0.242	0.368	0.321	0.094	0.081	0.170	0.135
1/2	0.5000	20	0.750	0.710	0.297	0.273	0.412	0.362	0.106	0.091	0.190	0.151
9/16	0.5625	18	0.812	0.768	0.336	0.308	0.466	0.410	0.118	0.102	0.214	0.172
5/8	0.6250	18	0.875	0.827	0.375	0.345	0.521	0.461	0.133	0.116	0.240	0.193
3/4	0.7500	16	1.000	0.945	0.441	0.406	0.612	0.542	0.149	0.131	0.281	0.226

Nominal Diameter

TPI

Head Diameter, dk

Head Side Height, H

Total Head Height, k

Slot Width, n

Slot Depth, t

max

min

max

min

max

min

max

min

max

min

0-80

0.0600

0.096

0.083

0.043

0.038

0.055

0.047

0.023

0.016

0.025

0.015

1-72

0.0730

0.118

0.104

0.053

0.045

0.066

0.058

0.026

0.019

0.031

0.020

2-64

0.0860

0.140

0.124

0.062

0.053

0.083

0.066

0.031

0.023

0.037

0.025

3-56

0.0990

0.161

0.145

0.070

0.061

0.095

0.077

0.035

0.027

0.043

0.030

4-48

0.1120

0.183

0.166

0.079

0.069

0.107

0.088

0.039

0.031

0.048

0.035

5-44

0.1250

0.205

0.187

0.088

0.078

0.120

0.100

0.043

0.035

0.054

0.040

6-40

0.1380

0.226

0.208

0.096

0.086

0.132

0.111

0.048

0.039

0.060

0.045

8-36

0.1640

0.270

0.250

0.113

0.102

0.156

0.133

0.054

0.045

0.071

0.054

10-32

0.1900

0.313

0.292

0.130

0.118

0.180

0.156

0.060

0.050

0.083

0.064

12-28

0.2160

0.357

0.334

0.148

0.134

0.205

0.178

0.067

0.056

0.094

0.074

1/4

0.2500

0.414

0.389

0.170

0.155

0.237

0.207

0.075

0.064

0.109

0.087

5/16

0.3125

0.518

0.490

0.211

0.194

0.295

0.262

0.084

0.072

0.137

0.110

3/8

0.3750

0.622

0.590

0.253

0.233

0.355

0.315

0.094

0.081

0.164

0.133

7/16

0.4375

0.625

0.589

0.265

0.242

0.368

0.321

0.094

0.081

0.170

0.135

1/2

0.5000

0.750

0.710

0.297

0.273

0.412

0.362

0.106

0.091

0.190

0.151

9/16

0.5625

0.812

0.768

0.336

0.308

0.466

0.410

0.118

0.102

0.214

0.172

5/8

0.6250

0.875

0.827

0.375

0.345

0.521

0.461

0.133

0.116

0.240

0.193

3/4

0.7500

1.000

0.945

0.441

0.406

0.612

0.542

0.149

0.131

0.281

0.226

ASME B18.6.3 - UNF Slotted Fillister Head Machine Screws

Figure 1: UNF Slotted Fillister Machine Screw

Table 1: Dimensions & Tolerances for UNF Slotted Fillister Machine Screws according to ASME B18.6.3 (inches)