Missing strut screws for GE fan…

[Todd Adornato]

I have a GE loop fan, Form S6 with the motor tag down the side of the housing, and which has a 16” cage with three struts.  I misplaced the screws that hold the struts in place; I tried figuring out what they were, but the closest I could get was a #10-24 thread, and that seemed a bit loose.  Is the thread an esoteric one, are the screws brass, and what is the proper length?   Thanks!

[Steve Rockwell]

          300,000 motors possibly separate the two tags' serial numbers,

but screws presumably did not change within Form S...

        12-28, brass, and 7/16" answer your questions; whether esoteric or not, someone else can answer that one...

[Mark Olson]

12-28 is an "esoteric" size and General Electric had a penchant for using such odd ball thread sizes on many of their products, not just fans, for reasons inexplicable to me.

[Todd Adornato]

Well, 12-28 is an esoteric enough size that I don’t have it in my collection of thread gauges 😁   Just for grins, I removed the three strut screws from a GE AO fan and tried those, but the thread is the wrong pitch.   I hit on the idea of loosely fitting taps from a tap and die set into the holes, and I found a 12-24 tap to fit perfectly.  Did GE switch to that size later in the Form S production run?

[Edward Kowalke]

I though they used 1/4"-24.

[Anthony Lindsey]

I have a 16" S1 missing struts/cage. I haven't found a matching screw yet.   And i have tried AOU,  BMY,  SMY and pancake screws.

[Anthony Lindsey]

This one

[Edward Kowalke]

I just pulled the brass strut to motor screw out of a 16" S-1  2 star. 7/16" long with a lock washer. #12-24, a tap threads in easily but a die did not thread onto the screw without friction. Also pulled a screw out of a 16" AC-1 brass bell and it is a 3/8" long (no washer) 1/4-24

[Todd Adornato]

Thanks for the info!   Looks like GE played fast and loose with thread sizes over the pre-WW2 years.

Edited September 10, 2023 by Todd Adornato

[Edward Kowalke]

I would not be surprised if the screw that did not accept the 12-24 tap is actually a 13-24 size.

[Steve Stephens]

6 hours ago, Todd Adornato said:

Thanks for the info!   Looks like GE played fast and loose with thread sizes over the pre-WW2 years.

Back in the earlier GE days the standards for threads were not well developed and GE still used their unique threads.

[Todd Adornato]

Well, I took a chance on some slotted brass bolts, 12-24 x 3/4” long, which were the closest I could find to the “factory” size, and I used a Dremel tool to trim three of the bolts.   They fit perfectly, and now the cage is snug once more.   Bonus:  the bolts already looked somewhat aged, not at all like the shiny bling of newly minted brass fasteners, so they don’t stand out overly much against the original patina of the fan housing.  So at least for my S6 GE fan, 12-24 is the proper size for the strut bolts.