Since the distance to the target wall surface is about 50 mm, and the thickness of the wall surface is about 100 mm, the length is insufficient with a normal drill, so since the item purchased this time is 250 mm, it can be opened without problem I am satisfied because I was able to do it. (In fact this time we have not used it because of purchase for when we need to expand the diameter of the hole opened with 5 mm long long straight drill (LSD).)