I actually used both, one on male and other one on female side. Thank youEverbilt 1/4 in. OD Compression Brass Cap Fitting 801129 - The Home Depot
These Brass Compression Caps are made for low to mid pressure applications. They conform to NSF 61 and 372. The caps are designed to fit the outside of tubes and threaded on the inside and feature a lead-free,www.homedepot.com
That fitting is likely not tapered thread, so you might want to put a few good turns of teflon tape or pipe dope on the threads .