Can I use a 1/4 inch drill bit instead of 5 mm?

Not if the hole must be exact. 5 mm = 0.1969 in, while 1/4 in = 6.35 mm — about 1.35 mm larger. For clearance holes that extra play may be fine; for close-fit fasteners or dowels, use a true 5 mm bit.

Is 13 mm the same as 1/2 inch?

Almost, but not exactly. 1/2 in = 12.7 mm, so 13 mm is 0.3 mm larger. On sockets and wrenches that gap can matter for bolt heads — prefer the matching system when torque or fit is critical.

When should I buy metric drill bits instead of fractional inch?

Buy metric when the drawing, fastener, or material is specified in millimeters (most ISO/metric hardware). Approximate with the nearest 1/64 only for non-critical clearance or woodwork where a fraction of a millimeter does not affect strength or fit.

What SAE socket is closest to 17 mm?

11/16 in (17.46 mm) is the closest SAE size, but it is about 0.46 mm larger than a 17 mm bolt head — loose enough to round the corners under torque. Use a true 17 mm socket or wrench.

Can I use a 3/8 inch socket on a 10 mm bolt?

No. 3/8 in = 9.525 mm, about 0.48 mm smaller than a 10 mm hex, so it will not go on. The next SAE size up, 7/16 in (11.11 mm), is about 1.1 mm oversize and will slip.

What fractional inch is closest to a 10 mm drill bit?

10 mm = 0.3937 in. The nearest 1/64 is 25/64 in (0.390625 in), about 0.08 mm undersize — usually acceptable for wood clearance, tighter for metal press-fits.

Drill Bit & Socket Sizes: mm to Inches

Metric bits and sockets rarely land on clean imperial fractions. Use decimal inches for math, the nearest 1/64 when you need a fractional chart size, and the error in mm to decide whether “close enough” is safe for the hole or fastener. Inch sizes convert the other way on the inch to mm hub (1 in = 25.4 mm).

Millimeters (mm) Inches (in) — decimals or fractions

Decimal inches: 0.2362
Nearest 1/64: 15/64 in (−0.047 mm)
Feet + inches: 0 ft 0.236 in

The inches fraction result is rounded to the nearest 1/64 fraction.

Metric drill & socket sizes → inches

Rows are generated from the shared conversion engine (1 in = 25.4 mm exact) plus drill-bits.json. The fraction column is the nearest 1/64 — not an exact equal. Where a size is commonly confused with a stock imperial (1/4, 1/2, 3/4, 1 in), the last column shows how far off that myth is in millimeters.

mm	decimal in	nearest 1/64	vs 1/64 (mm)	vs common imperial	nearest SAE socket	note
1	0.0394	3/64 in	+0.191 mm	—	—	Tiny pilot / PCB bit
1.5	0.0591	1/16 in	+0.087 mm	—	—	Small pilot
2	0.0787	5/64 in	-0.016 mm	—	—	Small screw pilot
2.5	0.0984	3/32 in	-0.119 mm	—	—	Light-duty bit
3	0.1181	1/8 in	+0.175 mm	1/8 in: -0.175 mm	—	Common metric; close to (not equal to) 1/8 in
3.5	0.1378	9/64 in	+0.072 mm	—	—	Common metric bit
4	0.1575	5/32 in	-0.031 mm	—	—	Common metric bit
4.5	0.1772	11/64 in	-0.134 mm	—	—	Common metric bit
5	0.1969	13/64 in	+0.159 mm	1/4 in: -1.350 mm	—	Often confused with 1/4 in
5.5	0.2165	7/32 in	+0.056 mm	—	7/32 in: +0.056 mm · near match	Between 7/32 and 1/4 in
6	0.2362	15/64 in	-0.047 mm	—	1/4 in: +0.350 mm · loose — can slip	Common metric bit / clearance
6.5	0.2559	1/4 in	-0.150 mm	1/4 in: +0.150 mm	1/4 in: -0.150 mm · too small — won't fit	Very near 1/4 in (6.35 mm)
7	0.2756	9/32 in	+0.144 mm	—	9/32 in: +0.144 mm · loose — can slip	Bit & small socket
8	0.3150	5/16 in	-0.062 mm	—	5/16 in: -0.063 mm · near match	Common bit; nearest 5/16 in
9	0.3543	23/64 in	+0.128 mm	—	11/32 in: -0.269 mm · too small — won't fit	Bit & socket
9.5	0.3740	3/8 in	+0.025 mm	3/8 in: -0.025 mm	3/8 in: +0.025 mm · near match	Near 3/8 in (9.525 mm)
10	0.3937	25/64 in	-0.078 mm	3/8 in: +0.475 mm	3/8 in: -0.475 mm · too small — won't fit	Common bit & socket; not 3/8 in
11	0.4331	7/16 in	+0.112 mm	—	7/16 in: +0.112 mm · loose — can slip	Socket / wrench size
12	0.4724	15/32 in	-0.094 mm	—	1/2 in: +0.700 mm · loose — can slip	Common bit & socket
13	0.5118	33/64 in	+0.097 mm	1/2 in: +0.300 mm	1/2 in: -0.300 mm · too small — won't fit	Near 1/2 in (12.7 mm)
14	0.5512	35/64 in	-0.109 mm	1 in: -11.400 mm	9/16 in: +0.287 mm · loose — can slip	Socket / wrench — not 1 inch
15	0.5906	19/32 in	+0.081 mm	—	19/32 in: +0.081 mm · near match	Socket size
16	0.6299	5/8 in	-0.125 mm	—	5/8 in: -0.125 mm · too small — won't fit	Larger bit / socket
17	0.6693	43/64 in	+0.066 mm	—	11/16 in: +0.462 mm · loose — can slip	Common metric socket; 11/16 in is loose
18	0.7087	45/64 in	-0.141 mm	—	11/16 in: -0.538 mm · too small — won't fit	Socket size
19	0.7480	3/4 in	+0.050 mm	3/4 in: -0.050 mm	3/4 in: +0.050 mm · near match	Near 3/4 in (19.05 mm)
20	0.7874	25/32 in	-0.156 mm	—	13/16 in: +0.637 mm · loose — can slip	Larger bit / socket
21	0.8268	53/64 in	+0.034 mm	—	13/16 in: -0.363 mm · too small — won't fit	Socket size
22	0.8661	55/64 in	-0.172 mm	—	7/8 in: +0.225 mm · loose — can slip	Socket size
24	0.9449	15/16 in	-0.188 mm	—	15/16 in: -0.188 mm · too small — won't fit	Large socket
25	0.9843	63/64 in	+0.003 mm	1 in: -0.400 mm	1 in: +0.400 mm · loose — can slip	Near 1 in (25.4 mm)

Positive “vs 1/64” means the nearest fraction is larger than the exact metric size; negative means smaller. The common-imperial column is metric minus imperial. The SAE socket column is SAE minus metric: a negative value means the SAE socket is smaller than the bolt head and will not go on; a positive value means it is loose and can round the head under torque.

When you must use metric bits — and when approximate imperial is OK

Use a true metric bit or socket when the drawing, fastener, or OEM part is specified in millimeters: ISO bolts, metric taps, European automotive sockets, and any press-fit or load-bearing hole where a few tenths of a millimeter change clearance or strength. Substituting 1/4 in for 5 mm (about 1.35 mm larger) is a common shop mistake that enlarges holes and loosens fits.

Approximate with the nearest 1/64 only for non-critical clearance — softwood pilots, cable pass-throughs, or rough carpentry — where the fraction of a millimeter shown in the table does not affect the job. Even then, prefer going slightly undersize for pilots and slightly oversize only when you need free play.

Sizes that look “almost imperial” still deserve a check: 13 mm vs 1/2 in (0.3 mm), 19 mm vs 3/4 in (~0.05 mm), and 25 mm vs 1 in (0.4 mm). On sockets and wrenches that small gap can round bolt heads; on drill bits it changes hole diameter permanently.

Metric bolt sizes at a glance

Common coarse-thread hex sizes from M3 to M20. This is a neighbor to drill bits and sockets — not a full fastener catalog. Confirm grade, length, thread series, and head style with the manufacturer.

Size	Nominal dia	inches (decimal)	nearest 1/64	coarse pitch	hex wrench (ISO)	hex wrench (DIN / shop)	clearance hole (normal)
M3	3 mm	0.1181	1/8 in	0.5 mm	5.5 mm	5.5 mm	3.4 mm
M4	4 mm	0.1575	5/32 in	0.7 mm	7 mm	7 mm	4.5 mm
M5	5 mm	0.1969	13/64 in	0.8 mm	8 mm	8 mm	5.5 mm
M6	6 mm	0.2362	15/64 in	1 mm	10 mm	10 mm	6.6 mm
M8	8 mm	0.3150	5/16 in	1.25 mm	13 mm	13 mm	9 mm
M10	10 mm	0.3937	25/64 in	1.5 mm	16 mm	17 mm · differs from ISO	11 mm
M12	12 mm	0.4724	15/32 in	1.75 mm	18 mm	19 mm · differs from ISO	13.5 mm
M14	14 mm	0.5512	35/64 in	2 mm	21 mm	22 mm · differs from ISO	15.5 mm
M16	16 mm	0.6299	5/8 in	2 mm	24 mm	24 mm	17.5 mm
M20	20 mm	0.7874	25/32 in	2.5 mm	30 mm	30 mm	22 mm

Pitch is the ISO 262 coarse series (the default when a drawing just says “M10”). Width across flats follows ISO / ASME B18.2.3.1M. Older DIN hex bolts and much shop hardware still use 17 mm / 19 mm / 22 mm wrenches for M10 / M12 / M14 — those three rows are the ones that do not match ISO. Clearance holes are ASME B18.2.8 normal fit minima, not tap-drill sizes.

Sources

Related mm to inches pages

Full formula, 0–100 mm chart, and “how far off” PAA answers live on the hub. Value pages deepen the sizes you check most often in the shop.

Also browse all length tools, the inch to mm hub, the mm to inches hub, and mm to inches fraction.

FAQ

Can I use a 1/4 inch drill bit instead of 5 mm?
Not if the hole must be exact. 5 mm = 0.1969 in, while 1/4 in = 6.35 mm — about 1.35 mm larger. For clearance holes that extra play may be fine; for close-fit fasteners or dowels, use a true 5 mm bit.
Is 13 mm the same as 1/2 inch?
Almost, but not exactly. 1/2 in = 12.7 mm, so 13 mm is 0.3 mm larger. On sockets and wrenches that gap can matter for bolt heads — prefer the matching system when torque or fit is critical.
When should I buy metric drill bits instead of fractional inch?
Buy metric when the drawing, fastener, or material is specified in millimeters (most ISO/metric hardware). Approximate with the nearest 1/64 only for non-critical clearance or woodwork where a fraction of a millimeter does not affect strength or fit.
What SAE socket is closest to 17 mm?
11/16 in (17.46 mm) is the closest SAE size, but it is about 0.46 mm larger than a 17 mm bolt head — loose enough to round the corners under torque. Use a true 17 mm socket or wrench.
Can I use a 3/8 inch socket on a 10 mm bolt?
No. 3/8 in = 9.525 mm, about 0.48 mm smaller than a 10 mm hex, so it will not go on. The next SAE size up, 7/16 in (11.11 mm), is about 1.1 mm oversize and will slip.
What fractional inch is closest to a 10 mm drill bit?
10 mm = 0.3937 in. The nearest 1/64 is 25/64 in (0.390625 in), about 0.08 mm undersize — usually acceptable for wood clearance, tighter for metal press-fits.