How many threads per inch on a #10 sheet metal screw?

12 on a Type A, 16 on a Type AB or Type B (ASME B18.6.3).

What is the difference between Type A and Type AB tapping screws?

Both have a sharp point; Type AB has the finer Type B thread — a #8 Type A has 15 threads per inch, a #8 Type AB 18. The standard recommends AB over A.

What size nut driver fits a hex washer head sheet metal screw?

#6 – 1/4″, #7 – 1/4″, #8 – 1/4″, #10 – 5/16″, #12 – 5/16″, 1/4″ – 3/8″, 5/16″ – 1/2″, 3/8″ – 9/16″ (ASME B18.6.3).

How big is the head on a #10 pan head sheet metal screw?

.373″ across at most; a Phillips pan head is up to .133″ tall.

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Tapping Screw Dimensions

Threads per inch, major diameter, head size and driver size for inch sheet metal (tapping) screws — Type A, AB and B, flat, oval, pan, truss, hex and hex washer heads — and self-drilling screws. ASME B18.6.3 (the tapping-screw tables that were ASME B18.6.4) and SAE J78.

A tapping screw makes its own thread as it goes in. Type A has a sharp point and a coarse, widely spaced thread, for thin sheet metal; the standard no longer recommends it and points to Type AB. Type AB has the same sharp point with the finer Type B thread. Type B has a blunt point, for a drilled or punched hole in heavier sheet metal, castings and plastics. A self-drilling (Tek) screw has a drill point that makes its own hole first. Sizes go by the number: #8 is about 0.16″, #10 about 0.19″; the larger sizes are sold as #14 (1/4″), #20 (5/16″) and #24 (3/8″) — for Type A the number is the size, for Type AB and B it is the fraction. Flat and oval heads sink into an 82° countersink; pan, truss, hex and hex washer heads sit on top.

The letters match the table columns.

Type A tapping screw threads — ASME B18.6.3 (inches)
Size	Threads per inch	Major dia max / min	Type AB thread at this length or shorter: pan, truss, hex heads	… flat, oval heads
#6	18	.141 / .136	1/4″	5/16″
#7	16	.158 / .152	5/16″	3/8″
#8	15	.168 / .162	3/8″	7/16″
#10	12	.194 / .188	3/8″	1/2″
#12	11	.221 / .215	7/16″	9/16″
#14	10	.254 / .248	1/2″	5/8″
#20	9	.333 / .327	11/16″	13/16″
#24	9	.390 / .383	3/4″	1″

A short Type A screw is made with the Type AB thread (next table) so it holds — the last two columns give the length. Sizes #2–#5 aren’t listed: only one of our sources has them.

Type AB and Type B tapping screw threads — ASME B18.6.3 (inches)
Size	Threads per inch	Major dia max / min
#2	32	.088 / .082
#4	24	.114 / .108
#5	20	.130 / .123
#6	20	.139 / .132
#7	19	.154 / .147
#8	18	.166 / .159
#10	16	.189 / .182
#12	14	.215 / .208
1/4″	14	.246 / .237
5/16″	12	.315 / .306
3/8″	12	.380 / .371

Type AB and Type B share one thread; AB has a sharp point, B a blunt one.

Flat head (82°) tapping screws — ASME B18.6.3 (inches)
Size	Head dia A max / min	Head height H max	Square drive
#2	.162 / .144	.051	—
#4	.212 / .191	.067	#0 square
#5	.237 / .215	.075	—
#6	.262 / .238	.083	#1 square
#7	.287 / .262	.091	—
#8	.312 / .285	.100	#2 square
#10	.362 / .333	.116	#2 square
#12	.412 / .380	.132	#3 square
#14	.462 / .427	.148	—
1/4″	.477 / .442	.153	#3 square
5/16″	.597 / .556	.191	#4 square
3/8″	.717 / .670	.230	—

Sits flush in an 82° countersink; length is measured overall. The Phillips driver size for flat heads isn’t on our chart yet — only one of our sources lists it.

Oval head (82°) tapping screws — ASME B18.6.3 (inches)
Size	Head dia A max / min	Side height H max	Overall head height max
#2	.162 / .144	.051	.080
#4	.212 / .191	.067	.104
#5	.237 / .215	.075	.116
#6	.262 / .238	.083	.128
#7	.287 / .262	.091	.140
#8	.312 / .285	.100	.152
#10	.362 / .333	.116	.176
#12	.412 / .380	.132	.200
#14	.462 / .427	.148	.224
1/4″	.477 / .442	.153	.232
5/16″	.597 / .556	.191	.290
3/8″	.717 / .670	.230	.347

A countersunk head with a raised dome; length is measured from the rim, the dome isn’t counted. Phillips driver size: not on our chart yet.

Pan head tapping screws, Phillips and square drive — ASME B18.6.3 (inches)
Size	Head dia A max / min	Head height H max / min	Phillips driver	Square driver
#2	.167 / .155	.062 / .053	—	—
#4	.219 / .205	.080 / .070	#1 Phillips	#0 square
#6	.270 / .256	.097 / .087	#2 Phillips	#1 square
#7	.296 / .281	.106 / .096	#2 Phillips	—
#8	.322 / .306	.115 / .105	#2 Phillips	#2 square
#10	.373 / .357	.133 / .122	#2 Phillips	#2 square
#12	.425 / .407	.151 / .139	#3 Phillips	#3 square
1/4″	.492 / .473	.175 / .162	#3 Phillips	#3 square
5/16″	.615 / .594	.218 / .203	—	—
3/8″	.740 / .716	.261 / .244	—	—

A recessed (Phillips or square) pan head is taller than a slotted one. #14 isn’t listed: only one of our sources has it.

Pan head tapping screws, slotted — ASME B18.6.3 (inches)
Size	Head dia A max / min	Head height H max / min
#2	.167 / .155	.053 / .045
#4	.219 / .205	.068 / .058
#5	.245 / .231	.075 / .065
#6	.270 / .256	.082 / .072
#7	.296 / .281	.089 / .079
#8	.322 / .306	.096 / .085
#10	.373 / .357	.110 / .099
#12	.425 / .407	.125 / .112
1/4″	.492 / .473	.144 / .130
5/16″	.615 / .594	.178 / .162
3/8″	.740 / .716	.212 / .195

Truss head tapping screws — ASME B18.6.3 (inches)
Size	Head dia A max / min	Head height H max / min	Phillips driver
#2	.194 / .180	.053 / .044	—
#4	.257 / .241	.069 / .059	#1 Phillips
#5	.289 / .272	.078 / .066	—
#6	.321 / .303	.086 / .074	#2 Phillips
#7	.352 / .333	.094 / .081	—
#8	.384 / .364	.102 / .088	#2 Phillips
#10	.448 / .425	.118 / .103	#2 Phillips
#12	.511 / .487	.134 / .118	—
#14	.557 / .530	.146 / .129	—
1/4″	.573 / .546	.150 / .133	#3 Phillips
5/16″	.698 / .666	.183 / .162	#4 Phillips
3/8″	.823 / .787	.215 / .191	—

A wide, low dome. A dash: our sources differ or only one lists it.

Hex washer head tapping and self-drilling screws — ASME B18.6.3 (inches)
Size	Nut driver	Across flats max / min	Head height max / min	Washer dia max / min
#4	—	— / .181	.060 / .049	.243 / .225
#6	1/4″	.250 / .244	.093 / .080	.328 / .302
#7	1/4″	.250 / .244	.093 / .080	.328 / .302
#8	1/4″	.250 / .244	.110 / .096	.348 / .322
#10	5/16″	.312 / .305	.120 / .105	.414 / .384
#12	5/16″	.312 / .305	.155 / .139	.432 / .398
#14	—	—	.190 / .172	.520 / .480
1/4″	3/8″	.375 / .367	.190 / .172	.520 / .480
5/16″	1/2″	.500 / .489	.230 / .208	.676 / .624
3/8″	9/16″	.562 / .551	.295 / .270	.780 / .720

The standard also allows a 7/16″ hex on 1/4″ and 5/16″ screws, so check the head. #14: our sources differ (3/8″ or 7/16″).

Hex head tapping screws — ASME B18.6.3 (inches)
Size	Nut driver	Across flats max / min	Head height max / min
#4	—	— / .181	.060 / .049
#6	1/4″	.250 / .244	.093 / .080
#7	1/4″	.250 / .244	.093 / .080
#8	1/4″	.250 / .244	.110 / .096
#10	5/16″	.312 / .305	.120 / .105
#12	5/16″	.312 / .305	.155 / .139
#14	—	—	.190 / .172
1/4″	3/8″	.375 / .367	.190 / .172
5/16″	1/2″	.500 / .489	.230 / .208
3/8″	9/16″	.562 / .551	.295 / .270

Same hex as the hex washer head, without the washer.

Good to know

Hole size for a tapping screw depends on the metal and its thickness, so it isn’t on this chart — give us a call. Self-drilling screws use the hex washer head table above; their thread and how thick a steel each drill point drills (SAE J78) aren’t on the chart yet — only one of our sources lists them, and makers rate their points differently. Round and binding heads aren’t on the chart yet. How to measure a flush head is on How to Measure a Flat Head; heads that sit on top on How to Measure a Bolt.

Quick answers

How many threads per inch on a #10 sheet metal screw?: 12 on a Type A, 16 on a Type AB or Type B (ASME B18.6.3).
What is the difference between Type A and Type AB tapping screws?: Both have a sharp point; Type AB has the finer Type B thread — a #8 Type A has 15 threads per inch, a #8 Type AB 18. The standard recommends AB over A.
What size nut driver fits a hex washer head sheet metal screw?: #6 – 1/4″, #7 – 1/4″, #8 – 1/4″, #10 – 5/16″, #12 – 5/16″, 1/4″ – 3/8″, 5/16″ – 1/2″, 3/8″ – 9/16″ (ASME B18.6.3).
What Phillips bit fits a #8 pan head sheet metal screw?: A #2 Phillips (ASME B18.6.3).
How big is the head on a #10 pan head sheet metal screw?: .373″ across at most; a Phillips pan head is up to .133″ tall.

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