Rough in 1 1/2" male IPS with 1/2" to 1" of threads above the finished floor. All tubing for Sign of the Crab drains is 1 3/8", replicating the original size of these drains. Use the included 1 3/8" x 1 1/2" square cut reducing washer to connect these sets with a 1 1/2" drain. Other brands use 1 1/2" OD tubing and will not include or require the reducing washer. The rough in for the drain hole on the floor is a plumb line from the center of the roll rim on the tub to the floor and approximately 4" from the wall behind the tub.