Ever wondered what size leaf springs you have on your Squarebody truck? Here is some info I put together for another forum that obviously didn't appreciate it much. I have a K10 that I am converting to a K20. This research answered alot of my questions for me. Notice a C10 and a K20 are the only models that could possibly have either the 52 or the 56 inch springs depending on the RPO code and factory installed equipment. BTW, both frames C and K are punched to be able to accept both size springs. The spring hangers are the same for 52 or 56 inch springs. So if you want to change your spring size, simply grind off the rivets, and use grade 8 bolts to relocate your spring hangers in the other set of holes already punched in your frame from the factory. One of the many things I love about GM, making things very universal and interchangeable. But, do keep in mind, C and K frames do use differant spring hangers. So although you can move the hangers to change your spring size, you must use K hangers for the K frame, and C hangers for the C frame. Very simple if whatever truck you are working on, simply use the same hangers on the truck you are working on, and they can be relocated without any fabbing or welding whatsoever. Front Leaf Springs K10, K20, and K30 Use the same springs. Differance is, they come in 2 leaf, 3 leaf or 4 leaf set up. All 3 set ups are interchangeable between all 3 models. I'd imagine the K30 comes in the 4 leaf set up, but the K10 and K20 could be either the 2 or 3 set up depending on heavy duty RPO code or not. Rear Leaf Spring 2WD C10, C20, C30. C10 can be 52 inch or 56 inch springs. Depending on Heavy Duty RPO code. C20 is 56 inch springs. # of leafs and thickness of spring pack depends on RPO code, ie... Smooth Ride, Heavy Duty etc. C30 is 56 inch springs. # of leafs and thickness of spring pack depends on RPO code. 10 Leafs is Heavy Duty 1 ton. Rear Leaf Springs 4WD K10, K20, K30. K10 is 52 inch springs. # of leafs and thickness of pack depends on RPO code. K20 can be 52 inch or 56 inch springs. Depending on Heavy Duty RPO code or not. (Appears that 52 inch may be more common) K30 is 56 inch springs. # of leafs and thickness of spring pack depends on RPO code. So becasue I am converting my K10 to a K20, with drum to drum axle swaps, I am also moving the rear spring hangers on the K10 which currently has 52 inch 1/2 ton springs, and I will be installing heavier 56 inch springs off of a C20 donor truck. For my 85 K10, the master cylinder is also the same for either the K10 or K20.