William,It is very hard to come up with an exact size for a 16 gauge choke on a smith gun.The bore sizes varys so much.One of mine measures .646 while another measures .662 .What is important is the relationship between the bore size and the choke size.An industry standard for a 16 gauge would be .008-.010 IC and .016-.020 for a Mod.I hope that helps you some.Most 16 gauge smiths,except the very late ones have 2.562 inch length chambers,just another thing to check while you are at it.Good luck;Charlie.