Technical Threaded Dust Covers on Ford Axles. What years?

I went to replace the dust caps on an old Ford I Beam I am messing with and discovered rather than pressed in the caps screw in (female end on the cap). I was told when I bought the front end it was a 47 or 48 but a guy at the parts store told me the threaded dust caps were only on 42 and down Ford models. What is the truth of the matter?
Thanks.

 

My '41 had screw on covers, round spindle brake mount.

 

My experience has been that hub inside drum has screw in caps, and hub outside drum has push in caps

But thats just my limited experience

 

I remember "42 and earlier had screw in caps.

 

my 41 has screw in caps

 

1940 Fords have screw in caps also.

 

the axle doesn't have the extra hole so I know its not a 48 and the caps screw in so I am gonna guess from the length and shape its probably early 40s. I was told by a previous owner it came from a "48 coupe" dragged out of the woods on Lookout Mountain. My best guess is he probably mistook a 41 for a 48.

 

Also keep in mind the type of dust cap...or year of drum... does little to help identify the year of the I beam they all interchange therefore 48 drums don't mean 48 Ibeam. And i have 41's with the inner hub with a press cap. so it might be 39 40 only with the threaded cap

 

I used this chart which is floating around to determine it is not a 48.
The 48 had an extra hole which the others lack.

 

Here are the backing plates if that is any clue to it's age. It is mounted under a trailer at present.

 

39-41 type, I think

 

Thank you. You are likely correct.

 

Since all the base hydraulic brake parts are interchangeable between the 39-41 and 42-48 brake setups you can't guess which part you have by IDing just one part.
I've dismantled many 28-48 Fords and found many with mixed backing plate brake assemblies, spindles, hub/drum assemblies.

Spindles: 37-41 round flange, 42-48 square flange, or earlier mechanical brake spindles

Backing plates: 39-41 with shoe lower adjustments, 42-48 with fixed lower shoe studs

Hub/drum assemblies: 39 with wide five pattern drums, 40-41 with 5 on 5.5 pattern drums mounted over hub flange, 42-48 with 5 on 5.5 pattern drums mounted under hub flange

Hubs: rear using 28-36 big cage wheel bearing or rear using37-48 small cage wheel bearing

 

I have a inside hub like the 40-42 drum that takes the pressed in dust cap. It would be my guess it is from a very late brake drum made for the 40-42 maybe by an aftermarket supplier of drums. The Ford green parts book list the threaded cap B-1139 for 31-35, 68-1139 for 36-45 & 51A-1130 (no threads) for 46-48.