2 Buttress Threaded x 2 Slip Tailpiece Flat 417-5040. This is a flat tailpiece without a groove for an o-ring. This tailpiece type uses a flat gasket (sold separately). This is a heater...
1.5" Heater Tailpiece Grooved 417-4090 1-1/2" split nut tailpiece mbt threads and slip connection works with heater gaskets like 711-4000 gasket or 805-0224 o-ring