Measuring With a Shaft Key

Need to make a precise measurement or adjust a tool? Get yourself a set of square shaft keys.

Shaft keys are used in the world of machinery to connect a shaft to something that rotates but we won’t be using them for their intended purpose. Rather, we’ll make use of the fact that they are made in precise metric and imperial sizes to use them as a measurement aid.

Shaft keys come in different flavors and shapes including curved, square and tapered. We’re looking for the square ones. Every hardware store has a set of shaft keys in a dusty, seldom opened drawer. My local store carried shaft keys between 1/8″ and 1/2″. You can buy a whole set for mere dollars. I used a sharpie to mark the dimensions of my set of shaft keys.

I use them mostly for setting the depth of my router and table saw. Using your sense of touch, aided by a shaft key, is much more accurate than using your eyeballs and a ruler.

But I also found them handy for assembling a new fence over the weekend. I wanted 1/4 inch gaps between the fence slats and used a shaft key as a spacer when I assembled the fence.

Stuff the stockings of the accuracy challenged housemates on your Christmas shopping list with a set of shaft keys!

Thank you to Bob Van Dyke for initiating me into the mysteries of the shaft key.

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