;   Measure the width of the needle across the flats, the sides of the needle. This is the dimension of the needle that if it were too wide, would cause it not fit into the slot of the cylinder or dial.

   With the micrometer, you can also measure the slot width, but you have to do it indirectly. Push a needle into a slot with a single piece of paper behind it. Won't fit? Find a thinner paper, or just put a layer of paper on one side of the needle. If the needle is still very loose, find a thicker paper or double the one you have. When you get the needle to slide in the slot tight (but not jammed in) then the thickness of the paper plus the thickness of the needle should be the slot width.
   Slots are generally 0.003 to 0.006 inch larger than the needle width, but vary quite a bit from cylinder to cylinder and even slot to slot in a given cylinder.
   You should check the width of several slots on a cylinder to make sure you didn't get the only one that was extra wide or narrow.

Contributed by Ralph Kanko, October 7, 1999.