Amazon.com: SiYear 3.5mm 1/8 inch TRS Plug to 6.35mm 1/4 inch Jack and 3.5mm Female to 6.35 Male Plug Gold Plated Set Audio Stereo Adapter Converter for Headphone, Microphone (4 -Pack) : Electronics
Everbilt 1/8 in. Barb x 1/4 in. MIP Brass Adapter Fitting 800049 - The Home Depot
AKG 0018E03350 1/8" Female To 1/4" Male Headphone Adapter | Full Compass Systems
Sennheiser Universal 1/8" to 1/4" Headphone Adapter 549346 B&H
LTWFITTING 1/4 in. O.D. Comp x 1/8 in. MIP Brass Compression Adapter Fitting (5-Pack) HF684205 - The Home Depot
Proline Series 3/8-in x 1/4-in Compression Adapter Fitting in the Brass Fittings department at Lowes.com
LTWFITTING 1/8 in. x 1/4 in. I.D. Brass Hose Barb Reducer Splicer Fittings (50-Pack) HF3913R040250 - The Home Depot
1/4" NPT Male x 3/8" NPT Female Swivel Straight 1404-04-06 Adapter | NPT Female Swivel to NPT Male - Straight | NPT to NPT | Hydraulic Adapters & Fittings | Hydraulics | www.surpluscenter.com
Amazon.com: Viair 90001 1/8" Female BSP - 1/4" Male NPT Adaptor - 2 Piece : Tools & Home Improvement
1/8″ (3.5mm) Stereo Male to 1/4″ (6.3mm) Stereo Female Adapter – ProCAT