These are threaded plugs with a base which block the end of a circuit by fitting this plug with an Allen key. They are offered in yellow PE approximately RAL 1018.
Thanks to its Polyethylene (PE) material, this stopper is resistant to different acids, greases, oils, etc.
The base ensures a good seal. And this 6-sided cap corresponds to the 13 key.
These screw caps are particularly used in mechanics and in industrial fluids.