Westfield Fasteners Product Specification:

ASME B18.6.3 - UNC Slotted Fillister Head Machine Screws

This product guide contains the specification for UNC 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

UNC 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 B18.6.3 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 slotted fillister machine screws and decribes the form, dimensions and tolerances, starting from the thread diameter of gauge size 1, up to and including 3/4 inch.

The slot drive can have parallel or slightly tapered sides.

Table 1: Dimensions & Tolerances for UNC 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
1-64	0.0730	64	0.118	0.104	0.053	0.045	0.066	0.058	0.026	0.019	0.031	0.020
2-56	0.0860	56	0.140	0.124	0.062	0.053	0.083	0.066	0.031	0.023	0.037	0.025
3-48	0.0990	48	0.161	0.145	0.070	0.061	0.095	0.077	0.035	0.027	0.043	0.030
4-40	0.1120	40	0.183	0.166	0.079	0.069	0.107	0.088	0.039	0.031	0.048	0.035
5-40	0.1250	40	0.205	0.187	0.088	0.078	0.120	0.100	0.043	0.035	0.054	0.040
6-32	0.1380	32	0.226	0.208	0.096	0.086	0.132	0.111	0.048	0.039	0.060	0.045
8-32	0.1640	32	0.270	0.250	0.113	0.102	0.156	0.133	0.054	0.045	0.071	0.054
10-24	0.1900	24	0.313	0.292	0.130	0.118	0.180	0.156	0.060	0.050	0.083	0.064
12-24	0.2160	24	0.357	0.334	0.148	0.134	0.205	0.178	0.067	0.056	0.094	0.074
1/4	0.2500	20	0.414	0.389	0.170	0.155	0.237	0.207	0.075	0.064	0.109	0.087
5/16	0.3125	18	0.518	0.490	0.211	0.194	0.295	0.262	0.084	0.072	0.137	0.110
3/8	0.3750	16	0.622	0.590	0.253	0.233	0.355	0.315	0.094	0.081	0.164	0.133
7/16	0.4375	14	0.625	0.589	0.265	0.242	0.368	0.321	0.094	0.081	0.170	0.135
1/2	0.5000	13	0.750	0.710	0.297	0.273	0.412	0.362	0.106	0.091	0.190	0.151
9/16	0.5625	12	0.812	0.768	0.336	0.308	0.466	0.410	0.118	0.102	0.214	0.172
5/8	0.6250	11	0.875	0.827	0.375	0.345	0.521	0.461	0.133	0.116	0.240	0.193
3/4	0.7500	10	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

1-64

0.0730

0.118

0.104

0.053

0.045

0.066

0.058

0.026

0.019

0.031

0.020

2-56

0.0860

0.140

0.124

0.062

0.053

0.083

0.066

0.031

0.023

0.037

0.025

3-48

0.0990

0.161

0.145

0.070

0.061

0.095

0.077

0.035

0.027

0.043

0.030

4-40

0.1120

0.183

0.166

0.079

0.069

0.107

0.088

0.039

0.031

0.048

0.035

5-40

0.1250

0.205

0.187

0.088

0.078

0.120

0.100

0.043

0.035

0.054

0.040

6-32

0.1380

0.226

0.208

0.096

0.086

0.132

0.111

0.048

0.039

0.060

0.045

8-32

0.1640

0.270

0.250

0.113

0.102

0.156

0.133

0.054

0.045

0.071

0.054

10-24

0.1900

0.313

0.292

0.130

0.118

0.180

0.156

0.060

0.050

0.083

0.064

12-24

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 - UNC Slotted Fillister Head Machine Screws

Figure 1: UNC Slotted Fillister Machine Screw

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