Size of Beseler Negatran 35mm O-Ring?

Does anyone out there in APUGland know the actual inside diameter of the Beseler 35mm negatrans o-ring?
6 3/4"? 7"? Larger?

A 2005 post in Photo Net reported that.."A good replacment is Buna O-ring Part Number 2-166 from Marco Rubber and Plastics (www.marcorubber.com)- this has the same dimensions as the Beseler Part and costs well under $2 apiece depending on the quantity you buy."

I haven't had to try this out but you might look at that website. The original poster said that it worked fine as a replacement.

Bill Delehanty

Bill,

I read the same post and ordered the O-ring. They are too thick. Their o/s dia. is 6 3/4" but it was a real stretch to fit. It could be the extra thickness, thus the question. I can order the right dia., but I want to verify the length first.

The one I found from a local shop was listed as A-021163N7 6x6-3/16. I had all of the old ring and they matched it up. It seems to be a good fit.