DIY Screw size gage

**mklotz** · Dec 16, 2016, 02:55 PM

You reach into your box of assorted screws, pull one out that looks about right for the job at hand. Now, you need to know what size it is so you can select the right pilot drill to use. You could measure its diameter and then work backwards through the formula:

Diameter = 0.060 + 0.013*(screw number)

to find its number so you can use one of the tables below to determine the pilot hole size. You say you're not fond of inverting equations in your head? Well then, you need to make one of these handy little screw sizing gages...

Any piece of sheet steel will work; mine is 2" OD. My gage has the following layout...

N = screw number
D = screw diameter according to the formula above
X = drill used to drill hole (err slightly on high side to provide clearance)

Code:

N	  D		  X

4	0.112		#33
5	0.125		1/8
6	0.138		#28
7	0.151		#24
8	0.164		#19
9	0.177		#15
10	0.190		#11
12	0.216		7/32

Once drilled, stamp the screw number next to the drill.

Use is trivial. Simply drop the screw into the smallest hole it will fit and read off the screw number.

You may want to gang drill several gages; the workbench and each tool bag should have one.

[I believe there is such a thing as a #14 screw but I've never seen one. If you use that size in what you do, include a hole for it too.]

-----------------------------------------------------------------

WOOD SCREW DATA

N = NOMINAL SIZE
T = THREADS PER INCH
D = DIAMETER OF UNTHREADED ROOT (in)
B = BODY DRILL SIZE (in)
S = PILOT DRILL SIZE IN SOFT WOOD (in)
H = PILOT DRILL SIZE IN HARD WOOD (in)

Code:

 N	 T	  D		B	 S	 H	  B	  S	  H
-------------------------------------------------------------------------------
 0	32	.060		52	75	66
 1	28	.073		47	71	57
 2	26	.086		42	65	54
 3	24	.099		37	58	53
 4	22	.112		32	55	51	1/8	1/16	5/64
 5	20	.125		30	53	47	9/64	5/64	3/32
 6	18	.138		27	52	44	9/64	5/64	3/32
 7	16	.151		22	51	39	5/32	3/32	7/64
 8	15	.164		18	48	35	11/64	3/32	7/64
 9	14	.177		14	45	33	3/16	7/64	1/8
10	13	.190		10	43	31	3/16	7/64	1/8
11		.203		4	40	29
12	11	.216		2	38	25	7/32	1/8	5/32
14	10	.242		D	32	14
16	 9	.268		I	29	10
18	 8	.294		N	26	6
20	 8	.320		P	19	3
24	 7	.372		V	15	D

Recommended Drill Sizes for Self-Tapping Screws (Sheet Metal)

N = Number
T = Threads per inch
OD = Outside Diameter
A = Drill for heavy metals
B = Drill for light metals

Code:

N      T    OD   A   B
2     32  .086  49  49
4     24  .112  41  41
5     20  .125  36  36
6     20  .138  32  32
7     19  .151  30  30
8     18  .164  28  29
10    16  .190  20  21
12    14  .216  13  14
1/4   14  .250  3   4
5/16  12  .313  I   H
3/8   12  .375  R   Q

**DIYer** · Dec 17, 2016, 08:12 AM

Thanks mklotz! We've added your Screw Size Gauge to our Measuring and Marking category,
as well as to your builder page: mklotz's Homemade Tools. Your receipt:

Screw Size Gauge by mklotz

tags: gauge