Accuracy International muzzle thread protectors to suit the standard Accuracy International spigot type M18x1.5mm thread.
I have always machined these from 6082T6 aluminium and indeed the one fitted to my rifle is several years old now and still going strong. However this time I have opted for 316 stainless which does take a bit longer to produce however they are probably more robust and they should last a lifetime.
Overall length is 35,0mm so it covers the full length of the spigot and thread, stops flush with the crown and is threaded 18x1,5mm.
I cannot think of a better way of protection your Accuracy International muzzle thread at the range and in the cabinet.