The 3" Triclover (TC) medium weld flange is typically welded into a sidewall of a vessel where you need a port. If you're building a brewery based on the sanitary/triclover method of device attachment, you'll have these all over the place. The tube OD is 3", the flange measures 3.5", and the overall length is .5" which is as short as you can go and still leave enough room for the clamp to attach. These are extremely high quality machined pieces, polished to perfection.