Mainspring Winder Clock Key Tool 5 Sizes Jewelers Go to amazon.com Related posts How to buy the best grandfather clock parts? DescriptionNew 5 Sided Clock Key. This is a new 5 sided clock key. The sizes are: Size 3, 3.00 mm. Size 5, 3.50 mm. Size 7, 4.00 mm. Size 9, 4.50 mm. Size 11, 5.00 mm.