I received a set of drawings for a tower mod that required replacing the diagonal pipes. The diagonals that were existing were fabricated from 3? pipe and the new modification required changing out the diagonals from 0? ? 80? and replacing with 3.5? pipe. The bottom diagonal ended up being longer than 21?, which required us to fabricate in 2 pieces like the existing ones. We went to the site and measured all the diagonals, fabricated them and sent them out for galvanizing. When they returned from galvanizing we mobilized to the site and started changing them out. The pipe diagonals we were installing were ½? larger in diameter which from center would only be ¼?. Needless to say none of the K bracing fit. It was very close but would not bolt up. Instead of calling me, my men decided to cut the K bracing tabs loose and move them about ½? off center and re-weld them, then the K braces would fit. Each diagonal had an upper and lower K so they moved the upper one to the left and the bottom one to the right. Good thinking on their part, however it was not what the Engineer had in mind. We notified the Engineer we had completed it and were ready for an inspection. When the Inspector came to the site he just kept looking at the diagonals and finally said something doesn?t look quite right. My men explained that because the pipe was larger in diameter that the K braces would only fit the way they installed them. When I was told about the situation, I was really upset with myself for not catching what was an obvious mistake on the drawings. We took full responsibility and shortened everyone of the K braces removed the tabs and installed them correctly. I?ve caught this on at least 2 other drawings since then. An expensive lesson such as that is hard to forget.