This is a spare bit. I've had a lot of problems with these breaks as they don't remove chips very well and tend to get hot which can cause severe bluing of the steel. They will break or break eventually and are a cheaper alternative to buying the whole unit as the countersink seems to have held up very well to me over time. I had many problems with these replacement parts as they were not perfectly straight and wobbled with use. I got 2 in a row and contacted Dewalt support. They sent me 2 replacements which looked fine but I got another one from Revain. This is not Revain's fault, but I recommend contacting Dewalt directly if you have any problems.