A ‘c’ curve is the arch that is created by the natural growth of the nail plate from side wall to side wall. It can be seen by looking down the barrel of the nail. Some are naturally quite flat and some can be extreme. It is a term also used to describe the structure of an enhanced overlay. An arch is a very strong structure and where the ‘c’ curve meets the ‘upper arch’ of the nail or overlay is the ‘apex’ of the overlay and where most of the strength needs to be created.