25.4 Since the impact socket for insertion angle is rare, there is a strong tendency that prices are high anywhere. Makita made is the cheapest, but it is rarely stocked in Makita's warehouse unless you ask the manufacturer. If it is KTC, the quality is good as it is certain. So I do not wish to continue purchasing. It is my life. Although it is a minor product at rare, I think the price of Monotaro is the cheapest. If you explain to someone you do not know, this inner socket can be considered as the shape of a female female. For normal work, we also use a socket of a different size and normal shape. There is also a combination socket that fulfills the function of two (outer socket + inner socket) for one piece, so it is uneasy at high torque 25.4 and it can not be used depending on the depth shape In some cases, it is better to consider.