Head diameter, head height and Phillips driver size for inch machine screws — flat, oval, pan, round, truss, fillister, binding and hex heads, Phillips and slotted, #2 to 1/2″. ASME B18.6.3.
A machine screw is sized by its thread: #10-24 is a #10 screw with 24 threads per inch. Flat heads sink flush into a countersink, so they’re measured overall; oval heads are measured from the rim, where the dome meets the cone — the dome isn’t counted; pan, round, truss, fillister, binding and hex heads sit on top and are measured under the head. Flat and round heads are the same size Phillips or slotted; a Phillips pan head is taller than a slotted one.
Letters match the table columns: A head diameter, H head height.
| Size | Head dia A max / min | Head height H max | Phillips driver |
|---|---|---|---|
| #2 | .162 / .144 | .051 | #1 |
| #3 | .187 / .167 | .059 | #1 |
| #4 | .212 / .191 | .067 | #1 |
| #5 | .237 / .215 | .075 | #2 |
| #6 | .262 / .238 | .083 | #2 |
| #8 | .312 / .285 | .100 | #2 |
| #10 | .362 / .333 | .116 | #2 |
| #12 | .412 / .380 | .132 | #3 |
| 1/4″ | .477 / — | .153 | #3 |
| 5/16″ | .597 / — | .191 | #4 |
| 3/8″ | .717 / .670 | .230 | #4 |
| 1/2″ | .815 / .765 | .223 | — |
Fits an 82° countersink. Same head for Phillips and slotted.
| Size | Head dia A max / min | Head height H (ref) |
|---|---|---|
| #4 | .212 / .188 | .049 |
| #6 | .262 / .235 | .060 |
| #8 | .312 / .282 | .072 |
| #10 | .362 / .329 | .083 |
| 1/4″ | .477 / .437 | .110 |
| 5/16″ | .597 / .550 | .138 |
| 3/8″ | .717 / .662 | .165 |
Fits a 100° countersink (sheet metal, aircraft work) — a wider, shallower head than the 82° flat. Same head for Phillips and slotted; length is overall.
| Size | Head dia A max | Head height H max | Phillips driver |
|---|---|---|---|
| #2 | .167 | .062 | #1 |
| #3 | .193 | .071 | #1 |
| #4 | .219 | .080 | #1 |
| #5 | .245 | .089 | #2 |
| #6 | .270 | .097 | #2 |
| #8 | .322 | .115 | #2 |
| #10 | .373 | .133 | #2 |
| #12 | .425 | .151 | #3 |
| 1/4″ | .492 | .175 | #3 |
| 5/16″ | .615 | .218 | #4 |
| 3/8″ | .740 | .261 | #4 |
Maximum sizes. The Phillips pan head is taller than the slotted one below.
| Size | Head dia A max / min | Head height H max / min |
|---|---|---|
| #2 | .167 / .155 | .053 / .045 |
| #3 | .193 / .180 | .060 / .051 |
| #4 | .219 / .205 | .068 / .058 |
| #5 | .245 / .231 | .075 / .065 |
| #6 | .270 / .256 | .082 / .072 |
| #8 | .322 / .306 | .096 / .085 |
| #10 | .373 / .357 | .110 / .099 |
| #12 | .425 / .407 | .125 / .112 |
| 1/4″ | .492 / .473 | .144 / .130 |
| 5/16″ | .615 / — | .178 / — |
| 3/8″ | .740 / .716 | .212 / .195 |
| 1/2″ | .987 / .958 | .281 / .260 |
| Size | Head dia A max / min | Head height H max / min |
|---|---|---|
| #2 | .162 / .146 | .069 / .059 |
| #3 | .187 / .169 | .078 / — |
| #4 | .211 / .193 | .086 / .075 |
| #5 | .236 / .217 | .095 / .083 |
| #6 | .260 / .240 | .103 / .091 |
| #8 | .309 / .287 | .120 / .107 |
| #10 | .359 / .334 | .137 / .123 |
| #12 | .408 / .382 | .153 / .139 |
| 1/4″ | .472 / .443 | .175 / .160 |
| 5/16″ | .590 / — | .216 / — |
| 3/8″ | .708 / .670 | .256 / .237 |
| 1/2″ | .813 / .766 | .355 / .332 |
Same head for Phillips and slotted. A dash: our sources differ or only one has it — give us a call at 405-670-1234.
| Size | Head dia A max / min | Head height H max / min | Phillips driver |
|---|---|---|---|
| #2 | .194 / .180 | .053 / .044 | — |
| #3 | .226 / .211 | .061 / .051 | — |
| #4 | .257 / .241 | .069 / .059 | — |
| #5 | .289 / .272 | .078 / .066 | — |
| #6 | .321 / .303 | .086 / .074 | #2 |
| #8 | .384 / .364 | .102 / .088 | #2 |
| #10 | .448 / .425 | .118 / .103 | #2 |
| #12 | .511 / .487 | .134 / .118 | — |
| 1/4″ | .573 / .546 | .150 / .133 | #3 |
| 5/16″ | .698 / — | .183 / — | #4 |
| 3/8″ | .823 / .787 | .215 / .191 | #4 |
A wide, low dome. Same head for Phillips and slotted.
| Size | Head dia A max | Overall head height H max |
|---|---|---|
| #2 | .140 | .083 |
| #3 | .161 | .095 |
| #4 | .183 | .107 |
| #5 | .205 | .120 |
| #6 | — | .132 |
| #8 | .270 | .156 |
| #10 | .313 | .180 |
| #12 | .357 | .205 |
| 1/4″ | .414 | .237 |
| 3/8″ | .622 | .355 |
A tall, narrow head. Maximum sizes; height is to the top of the rounded crown. #6 head diameter: our sources differ. A Phillips fillister has the same head; its Phillips driver size isn’t on our chart.
| Size | Head dia A max / min | Overall head height max / min |
|---|---|---|
| #2 | .181 / .171 | .050 / .043 |
| #3 | .208 / .197 | .059 / .052 |
| #4 | .235 / .223 | .068 / .061 |
| #5 | .263 / .249 | .078 / .069 |
| #6 | .290 / .275 | .087 / .078 |
| #8 | .344 / .326 | .105 / .095 |
| #10 | .399 / .378 | .123 / .112 |
| #12 | .454 / .430 | .141 / .130 |
| 1/4″ | .525 / .498 | .165 / .152 |
| Size | Wrench / nut driver | Across flats max / min | Head height max / min |
|---|---|---|---|
| #2 | 1/8″ | .125 / .120 | .050 / .040 |
| #4 | 3/16″ | .188 / .181 | .060 / .049 |
| #5 | 3/16″ | .188 / .181 | .070 / .058 |
| #6 | 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 |
| 1/4″ | 3/8″ | .375 / .367 | .190 / .172 |
| 3/8″ | 9/16″ | .562 / .551 | .295 / .270 |
Same hex for plain hex and hex washer heads, slotted or not. The washer diameter isn’t on this chart yet.
| Size | Head dia A max | Overall head height max |
|---|---|---|
| #2 | .162 | .080 |
| #3 | — | .092 |
| #4 | .212 | .104 |
| #5 | .237 | .116 |
| #6 | .262 | .128 |
| #8 | .312 | .152 |
| #10 | .362 | .176 |
| #12 | — | .200 |
| 1/4″ | .477 | .232 |
| 3/8″ | — | .347 |
| 1/2″ | — | .354 |
A countersunk head with a raised dome. Length is measured from the rim, not the top of the dome; overall height includes the dome. Maximum sizes.
Measuring and threads
Thread pitch and tap drill for every size are on the thread pitch chart. 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
- What size Phillips bit fits a #10 machine screw?
- A #2 Phillips for a #10 pan or flat head machine screw.
- What Phillips driver goes with each pan head machine screw?
- #2 – #1, #3 – #1, #4 – #1, #5 – #2, #6 – #2, #8 – #2, #10 – #2, #12 – #3, 1/4″ – #3, 5/16″ – #4, 3/8″ – #4.
- How big is the head on a 1/4-20 flat head machine screw?
- .477″ across at most and .153″ tall; it fits an 82° countersink.
- Is a Phillips pan head taller than a slotted pan head?
- Yes — a #10 Phillips pan head is up to .133″ tall, a slotted one .110″.
- How do you measure a flat head machine screw?
- Overall — from the top of the head to the tip, because the head sinks flush. Pan and round heads are measured from under the head.
- How do you measure an oval head machine screw?
- From the rim — the widest edge of the head, where the dome meets the cone — to the tip. The dome isn’t counted.