Honda NT650 Hawk GT chain slack tool

So you've lost the chain slack gauge, or didn't get one with your bike.

You can make one!

Here's a picture of the whole thing.

and here's a closeup of the business end.

Peter Paulovits in Germany reminded me that most of the world is metric, and supplied the appropriate numbers:

A = 33 mm1.3 inches or 1-5/16 "
B = 43 mm1.7 inches or 1-11/16 "
C = 53 mm2.1 inches or 2-2/32 "

And here's how to use it.