For added strength and statbility on larger sized frames, a set of Cross Braces (B and C) is required for stretcher bars that are 48" and above; that extend over in two directions and up to 84" x 84".You must have one brace type B and one one brace type C for a Cross Brace.  All products listed are usually of a large weight and size. Due to this fact, extra freight charges will be calculated upon check out.