Amazon.com: VCE 1/4" to 1/8" Adapter, 3.5mm 1/8 inch Male to 6.35mm 1/4 inch Female Audio Jack Gold Plated Adapter for Amplifiers, Guitar, Home Theater Devices, Laptop, Headphones - 8 inch : Electronics
1/8" Male NPT x 1/4" Flare (SAE) Brass Adapter
Everbilt 1/8 in. Barb x 1/4 in. MIP Brass Adapter Fitting 800049 - The Home Depot
Comprehensive Stereo 1/4" Male to Stereo 1/8" (3.5mm) SPP-MJS
Everbilt 1/4 in. OD Compression x 1/8 in. MIP Brass Adapter Fitting 800729 - The Home Depot