CPR Aquatic 4 Count Slip by Slip ABS Bulkheads for Aquarium Filters, 1-Inch Pack of 4 complete units 1" ABS Bulkhead Slip x Slip (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