Hansohn. I have a Sig MCX k with a barrel threaded for M13. 5x1LH.  At the moment the only suppressor I have is a silencerco hybrid.  Do you sell a mount I can use for this?  In the near future I'm planning on moving up to a true 9m can like yhm r9.

Also, how do I keep an end cap from twisting off when the end cap is RH but the barrel is LH?

I recommend the Rearden Flash hider with SIG taper  and the Rearden Atlas ASR adapter.   Another option is the Dead Air Xeno Adapter  and Dead Air Xeno Wee Brake .

If the mounts are torqued properly, there shouldn't be any issue with parts coming unthreaded.

Hope this helps!

Currently have my SiCo hybrrid on a cz scorpion with a 1/2X28 direct thread adaptor I purchased from you.  Will the Rearden Flash hider with SIG taper you suggested fit that or the stock rear end cap or do I need something else.  

Sorry for all the questions, I just don't want to have to make multiple orders to get this running.

Not a problem.  You will also need the Rearden Atlas  if you use the Rearden flash hider.  The good thing about this set up is you can put Rearden muzzle devices on all of your firearms and be able to use any silencer that has the Rearden Atlas installed.