looked this up for the stock tanks :
Military Description:
TANK,PRESSURE PRIMARY
National Stock Number (NSN): 2530-00-753-9241, 2530007539241
Federal Supply Class (FSC): 2530 (Vehicular Brake, Steering, Axle, Wheel and Track Components-10)
National Item Identification Number (NIIN): 007539241
Federal Stock Number (FSN): 2530-753-9241, 25307539241
Technical Characteristics:
Capacity (AXQD):995.000 cubic inches
End Thickness (AXPW): 0.062 inches nominal
End Shape And Location (AXPT): Convex both ends
For Use With/On (AGAV): Carrier, cargo 6-ton (m548 & m548a1); truck, cargo, dropside 2 1/2-ton 6x6 w/e
Material (MATT): Steel
Mounting Base (AXQE): Not included
Opening Characteristic (AXQB): Threaded and threaded
Opening Location (AXQA):` One on each end and on side
Opening Quantity (AXPY): 3 and 1
Opening Size (AXPZ): 0.375 inches and 0.250 inches
Outer Shell Material Thickness (AXQC): 0.062 inches nominal
Overall Diameter (ADAV): 7.000 inches nominal
FSC Application Data (ZZZV): Brake,air,vehicular
Screw Thread Series Designator (AJYP): Npt and npt
Overall Length (ABHP): 29.000 inches nominal
Thread Direction (AAJF): Right-hand
Thread Size (ABUJ): 3/8-18 and 1/4-18
National Stock Number (NSN) 2530-00-753-9241