tosefos chullin 50 says cicumference of sela is a tefach selaim of bar kochba have diameter of 26 mm this should prove(1)tosefos is right unlike rashi (there) (2) r chaim naeh is right (tefach is 80 mm) (3) a gris is smaller than a penny (plaisi 190 14 proves that a gris is less than half a sela). is there any way out of this? thank you!
y genack, Queens
All of the above is based on saying that the Sela referred to by Tosfos must have the same diameter as that of the Sela of Bar Kochba. This is not necessarily true, as is evident throughout Shas that the same denomination of coins throughout history have differed in weight and measurement. Indeed, in the Sefer Midos v'Shiurei Torah (pg. 166) he discusses this at length, and shows records of various Sela'im with very different diameters.
All the best,
Yaakov Montrose