Just FYI, I came across this in doing some research for a buddy of mine at work...
Don't know if that's helpful or not...
(6) “Illegal Knife” means a: (A) knife with a blade over five and one half inches; Rainer v. State, 763 S.W.2d 615 (Tex. App.-Eastland 1989, pet. ref’d) To determine length, measure entire length of blade past handle, not just the sharpened portion of the blade. Same result in McMurrough v. State, 995 S.W.2d 944 (Tex. App.-Ft. Worth 1999).
Don't know if that's helpful or not...