CPR Aquatic 4 Count Thread by Thread ABS Bulkheads for Aquarium Filters, 0.75-Inch Pack of 4 complete units 3/4" ABS Bulkhead Thread (FPT) x Thread (FPT) - (flange x stem) Fits standard schedule 40 or 80 PVC pipe and fittings; Nominal Pipe Size and Standard Pipe Thread apply to inside; outside threads are not standard PT Look for the CPR UPC label. Don't accept imitations