3/8 IPS (odd size) x 1/4 IPS.
These reducers have 5/8" outside diameter threads (3/8 IPS) to 1/2" diameter hole (works with 1/4 IPS pipe). Picture shows 2 pieces-priced each. The 3/8 IPS IS AN ODD SIZE FOR MAKING LAMPS.
$2 minimum charge for orders less than $20.
$.50 packing charge for each parts box.