OK Friends, This may be the wrong forum, but I bet I get an answer. I have owned a couple pistols for several years, have purchased a HP pistol and carbine within the last few months, but just ordered and recieved my first "brand new" shotgun this week. I am a complete newbie on them. I followed the manual and did the cleaning, lubing, and assembly as directed. The gun came with this tool or gauge as pictured, with no explanation as to WTF it is for. Anyone care to tell me what it is for? It is marked "plus, 12ga, and 20ga" as it tapers down. The gun is a Winchester 12Ga. SXP. Thanks.