4T please

I have a LEM stuffer and the tubes come in inch dimensions.
What size casing, 19 or 21 mm, will fit on my 1/2" OD- 3/8" ID tube?

Thanks

Thanks Glen, but a simple conversion is not the answer. While 19mm casings easily fit over a 1/2" tube when stretched out, the question is more centered around will the stacked, compressed, “out the the bag” casing slip in the tube. Not having any 21 or 19 mm collagen casing on hand to measure the inside diameter of the “out of package” casings, its hard to tell.
Several times I have heard Johnathan state that a 21 mm will fit over a 12 mm tube; I question if that is 12 mm ID or OD.
So, I will rephrase my question, Does anyone know what the ID of the 21 mm collagen casing and the ID of the 19 mm collagen casings are when they come out of the package, ready to slip on the stuffing tube? Mm or inch dimensions will be fine.

Thank you

PapaSop, wish it was that easy. 1/2” is the smallest I have. Would like to use the 19 mm but looks like I’ll just use the 21mm.