For rubber belts, Gates makes all the different sizes.  They still
make the 3L belts which are suitable for small suction pumps like the
box pump.  The 3L belt has a smaller cross section than the common 4L
(A) belts.  If the sheave on your box pump was intended for a V-belt,
a good replacement is the regular 3L belt (not the modern cog design).
It looks close to the older styles, and for this diameter the
horsepower rating is the same as the thicker 4L belt.

Gates regional telephone number: 214 342 9979

Brian Smith