Winding Key Sizes

	CLOCKS				WATCHES
	U.S. / English		Euro*		U.S. / English		Euro*
Key Number	Metric (mm)	Inches (.000)	Metric (mm)	Key Number	Metric (mm)	Inches (.000)	Metric (mm)
00000	1.6	0.063	...	00	0.95	0.037	2
0000	1.8	0.071	...	0	1	0.039	1.9
000	2	0.079	1.75	1	1.05	0.041	1.8
00	2.2	0.087	2	2	1.15	0.045	1.75
0	2.4	0.094	2.25	3	1.2	0.047	1.65
1	2.6	0.102	2.5	4	1.3	0.051	1.6
2	2.8	0.11	2.75	5	1.4	0.055	1.5
3	3	0.118	3	6	1.5	0.059	1.4
4	3.2	0.126	3.25	7	1.6	0.063	1.3
5	3.4	0.134	3.5	8	1.65	0.065	1.2
6	3.6	0.142	3.75	9	1.75	0.069	1.15
7	3.8	0.15	4	10	1.8	0.071	1.05
8	4	0.158	4.25	11	1.9	0.075	1
9	4.2	0.165	4.5	12	2	0.079	0.95
10	4.4	0.173	4.75
11	4.6	0.181	5
12	4.8	0.189	5.25
13	5	0.197	5.5
14	5.2	0.205	5.75
15	5.4	0.213	6
16	5.6	0.22	6.25
17	5.8	0.228	6.5
18	6	0.236	6.75
19	6.2	0.244	7
20	6.4	0.252	7.25
21	6.6	0.26	7.5
22	6.8	0.268	...
23	7	0.226	...
24	7.2	0.283	...
25	7.4	0.291	...

From The Clock Doc by Tom Roma

* A special thanks to This email address is being protected from spambots. You need JavaScript enabled to view it. for his help with these tables especially the addition of the European/Continental/Swiss range of key sizes. Harry also points out that sizes of keys from different manufacturers are not consistently accurate. The other thing, which adds to the difficulty of sizing, is that older clocks tend to have tapered winding squares, matched by tapered mortises in their (antique) winding keys. It is therefore sometimes a good idea to use a key that is a little undersize, and file it out to a taper, providing that there is sufficient wall thickness for safety.