I bought this wrench based on a review saying it would fit a collet nut on a 5C collet. With 10 seconds (literally) on a belt sander to round the outside edges of the pin, this wrench fits perfectly; just like the previous reviewer said it would. 5C collet block sets are sold with blocks and collet nuts, but do not come with a nut wrench. The nut is 42 mm in diameter or approximately 1.6535 inches. I used a Knipex water pump wrench to tighten the nut. But even with very careful work, theβ¦