Amazon.com : Camera Screw Adapter Thread 1/4" Male to 3/8" Female and 3/8" Male to 1/4" Female Adapter Set for Camera Monitor, Tripod, Mount : Electronics
CRAFTSMAN 1/4-in to 3/8-in Socket Adapter in the Socket Adapters department at Lowes.com
Threading Adapter, G 1/4 Male to NPT 3/8 Female
3/8" NPT Female to 1/4" NPT Male Brass Pipe Adaptor/Adapter Straight Reducer/Reducing Coupling Male to Female: Pipe Fittings: Amazon.com: Industrial & Scientific
Amazon.com: KOOTANS 3/8 NPT x 1/4 NPT Male Solid Brass Hex Nipples, Heavy Brass Pipe Adapter Fittings Reducing Nipples Connectors 4Pieces : Industrial & Scientific