This ingenious device protects the threads of disposable 1 pound propane bottles and helps prevent thread damage and seals out dirt. You will receive 2 caps per order. The Mac Caps makes a welcome addition to any camping gear, RV enthusiast, outdoorsmen, or home owner that needs to use a 1 lb. propane tanks. Now you can protect the threads of those tanks with the Mac Cap. Simply attach the Mac Cap to your 1 lb. tank when not in use to help prevent leaks and protect the threads. The Mac Cap is manufactured from the finest brass.