To those who wonder why: safety issue.
Just ask yourself why Discovery valves are pinned from both sides !!
The item is sold as a drop-in, screw in, whatever: you may do the math.
The seller entered the forum only intending to sell, not to join the community, he has acted plain rude and has no social skills at all.
I've deleted his topics and the ones posted by the people he sent here after being banned: check airgunhome and the Canadian airgun forum if you're interested in more info.
Edit: read this please
http://www.gatewaytoairguns.org/GTA/index.php/topic,15235.msg130074.html#msg130074