The shaft diameter is approximately 14 mm. This was purchased from a junk coffee sale at an ESP-affiliated store. My guess is that these were brought in for parts replacement and are leftover stock from the replaced parts. These are the type of tuners with two on each side, with two on the left side and one on the right side when viewed from the front. "HC37" is visible on the left side, and "27HC" is visible on the right side. There are no screws. The items for sale are only the tuners, washers, and nuts as shown in the photo. There are small scratches and scuffs, but the movement is smooth.