The length between the center of the two bolts is referred to as the center line.  The distance between the center of the tank holes must be within 1/32” of the center line measurement.

Items
B3540-51300BA1W

Aluminum Liquid Level Gage with Card Thermometer and Shut-off, 13” Centerline, Front Mount 1/2"-20

B3540-51300BB1W

Aluminum Liquid Level Gage with Card Thermometer and Shut-off, 13” Centerline, Back Mount 1/2"-20 with Nuts

B3540-51300BN1W

Aluminum Liquid Level Gage with Card Thermometer and Shut-off, 13” Centerline, 1/4" Male NPT Adapters

B3540-51300BN2W

Aluminum Liquid Level Gage with Card Thermometer and Shut-off, 13” Centerline, 3/8" Male NPT Adapters

B3540-51300BN3W

Aluminum Liquid Level Gage with Card Thermometer and Shut-off, 13” Centerline, 1/2" Male NPT Adapters
Centerline N/A 13"
Mounting N/A 1/2"-20 N/A 1/2"-20 with Nuts N/A 1/4" Male NPT Adapters N/A 3/8" Male NPT Adapters N/A 1/2" Male NPT Adapters
Feature N/A Card Thermometer, Shut-Off
Max Pressure N/A 175 PSI
Max Temperature N/A 225° F
Seals N/A Buna-N
Body Material N/A Aluminum