I Believe these are S351 channel balances they're stamped 16B but when you measure from metal edge to metal edge I get 17 inches so I don't know which size on the option chart 16 inch or 17 inch. I am the homeowner bought these in 2003 when we built the house I have other windows that are 23 27 28 with some having a B or a C after the number so I'll be ordering others I just need to get a reference on the numbers that are punched on the side of the balance to whether or not I use that for my length or the measurement from metal edge to metal edge I'm doing the stuff myself handy I know some people would probably hire somebody but I'm able to do this myself thanks for your help
Wayne