Some notes to get things started, and the reasons why this is all so complicated:
- The top should be flat.
- The slot should be perfectly perpendicular. Modern pan-head slotted screws are not made this way (see pics below)
- The vintage screws seem to be highly ferrous and are much more magnetically attractive than the modern screws.
- Although it’s hard to measure the slot, it seems to be a perfect fit for my Klein 601-4 3/16-inch Cabinet Tip Screwdriver and seems to fit with the highlighted ANSI spec below.
The ANSI Standard
Although there is an ANSI standard for machine screws (specifically ANSI B18.6.3-1972 (R1991)), and these vintage screws seem to fit within the range highlighted in the chart on the left (from thomasnet.com), there seems to be no accepted standard for what “pan head” really means. For example, the chart on the right, from almabolt.com shows that either of the highlighted shapes are acceptable, and the ANSI standard does not list detailed dimensions of the head such that a flat top surface is required aside from the picture. The problem seems to be that the more rounded variety is the one being manufactured today.
These are my own measurements based on vintage screws in my possession.
Photos I took showing the difference between modern pan-head screws and the vintage HB1 screws. All single-screw images are of the vintage sample.
As of June 2020, I have not found a source to replicate these screws. If you can make these, please let me know. I’m happy to buy 100 or more, and an twice that number if half the order can be finished in gold.