Yes, I'm just f^&*ing with you.
We have all seen some weird mis-stamps, overstrikes, hard-to-decipher codes, etc, but I have never seen an "F" before. And the "E" was nominally sans serif, anyway. That sucker has some pronounced serifs. Definitely odd. Especially because it is in a typical placement area for a date code and they were not in the habit of any other kinds of codes, especially in the 40's. Almost makes me want to say something was wrong with the die stamp that hour (day, etc) and they just improvised.
If you don't get too much response here, you may want to try asking on the dedicated 'Snap-on' thread. People who are only Watching their favorite threads and who don't scan the forum for new threads will see it there. You can find it very easily in the A-Z Index of Threads in the Sticky at the top of the forum titled READ B4 POSTING!