There are 2 ways of measuring for a proper bowl size fit. One way is using a string or a OD tape to measure the hose. Another way and most accurate is using a digital caliper to measure the inside of the bowl on the coupling.
Materials Needed To Get Started:
Hose and/or Coupling
Digital Caliper
Rope/String
Marker
OD Tape
Measuring Tape
Calculating A Hose Diameter Using A String
Place a lay flat hose on a flat smooth surface
Wrap the string around the hose
Keep the string running around the diameter straight and true
Mark the string across both ends
Lay out the sting next to a yard stick and tape measure
Read the length of the string from mark to mark
This will give you the circumference of the hose
Take this length and divide by PIE: 3.1416
This will give you the diameter of the hose
Calculating A Hose Diameter Using A OD Tape
Wrap the OD tape around the hose
Read the length of the string from mark to mark
This will give you the diameter of the hose
Calculating The Inside Diameter With A Digital Caliper
Place the inside tips of the caliper on the inside of the bowl (coupling)
Expand the tips of the caliper until they're fully extended to the bowl size
This will give you the correct size of the bowl needed
