I have three planes and four blades. The fourth blade has a cap, but no cap screw. A copy will be made from one of the three cap screws I have. The screw's overall length is 0.380". The slotted head is 0.197" thick leaving a screw length of 0.183". The head O.D. is 9/16" and the screw is 5/16-24. The 24 is assumed as a 5/16-18 nut was a no go. The slot is 1/16" wide.
A 1 3/4" length of 5/8" steel round was located in the scrap box. It was chucked in the three jaw chuck and after facing reduced to 9/16" for 1/2". A further reduction to 5/16" was done for the length of the threaded portion. A 0.030" deep thread relief was cut. The corners were chamfered. A 5/16-24 die was used to cut the threads. It was started in the lathe and then transferred to the vise. The part was returned to the lathe and parted off at length.
The screw was turned around in the chuck and attached to the four-sided indexing block. This was held in the milling vise on parallels. The plan does not show the depth of the cut through the head, 0.084". A 0.057" slitting saw was used to make the cut in 0.010" passes. They went well with cutting fluid. A little filing and the screw was complete.
