BrassCraft 3/8-in x 1/2-in Compression x Mip Adapter Fitting in the Brass Fittings department at Lowes.com
1/8" Female NPT X 1/4" Push Connect Adapter - John Guest - Bulk Reef Supply
Sennheiser Universal 1/8" to 1/4" Headphone Adapter 549346 B&H
Everbilt 1/8 in. Barb x 1/4 in. MIP Brass Adapter Fitting 800049 - The Home Depot
Threading Adapter, NPT 1/8 Male to G 1/4 Female
Female Pipe Reducer 3/8" to 1/4" Npt Adapter Coupler Brass Fitting Water Oil Gas | eBay
1/4" to 1/8" stereo adapter - Audeze LLC
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