Just caught this one. NOT A TA is correct, the 5" is a misnomer for our products. The actual diameter is slightly less. 3 3/8" cases with a 3 3/4" outer bezel diameter represent the second standard size that we offer. If 4" in particular is what you're looking for, we do offer that particular configuration in our Cobra Series:
http://www.autometer.com/cat_gaugeop.aspx?sid=52
These are designed to replicate the original instruments found in the Shelby Cobra and include the correct appearing reverse rotation mechanical speedometer. In order to run one of these a reversing adapter will be required. If you call our toll free tech line our staff can help you sort the pieces that would be required for installation and answer any questions that you may have. Hope that helps!
