Make a 1 inch by 3 inch plate of .75 mm aluminum or brass and cut a slot to gauge the hair. Make sure the entrance is rounded and the edges of the slot are sanded
very smooth to prevent damage to the hair. Mark your depths as needed.
To mark the depth of the slot for violin hank count 150 hairs, push them in tight and mark that line. For cello you might try 225 hairs and mark that line. These are basic lines and the hank you cut will vary with the bow you rehair.