sizes sorry if this sounds a bit thick but your key clamp 131-B I then go to get dimensions in PDF and when I do its saying 131-1 and there is a list but no 131-B ? so how do you know whats what then can you please let me know thanks Existing Answers Hi, thanks for your question. No, you aren't being thick, it isn't immediately obvious on the data sheet. The measurements for the clamps correspond as follows "B" size clamps are shown as "-2" on the datasheet. So for the 131B measurements you would look at the line marked 131-2. I hope this helps.