Aluminum frame single hung tilt windows from 1978, manufacturer unknown.

A handy person from mo says:

The windows use a 3/8 spiral balance 24in long with blue tips,and a sash weight of 15lbs, The pivot shoe measurements is 2" tall 1-1/4" wide and 9/16" thick, which matches the description of part# 15-121, however i read a post stating that part would not work with the 900 series spiral balance. 

My question is, will the 15-118 {which has the same measurements} or the 15-046 {with only a slight different in thickness} work with the 900 series spiral balance? As i would prefer if possible, to have the center notch in the pivot shoe to keep the alignment straight with the balance and window channel. 

please confirm the the correct replacement part numbers to match my needs that work in conjunction with each other. Thank You.

Thumbnail of the uploaded file named Pivot Shoe - Picture.jpg
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Paul from SWISCO responded:

Looking at your photo and reviewing all the information you provided, it seems you have an Acorn window that may be able to use our 15-015 pivot shoe along with the Series 900 spiral balance. The thickness of the pivot shoe is 17/32". You may want to confirm your pivot shoe dimensions just to be sure.

A handy person from mo says:
I remeasured the pivot shoe, and the original ones measure two inches tall, one and a quarter inch wide and seventeen thirty seconds thick,(2"T x 1 1/4xW X 17/32 T). S0 the 15-015 you mentioned may work. However i am concerned that it has two offset slots in the top of it to accept the ears of the spiral balance in either one which would push it either closer to the front or closer to the back of the pivot shoe and balance channel. please look at the new picture i sent and notice the slot is centered in the middle of the pivot shoe. if you have a pivot shoe that measures 1/2 thick with a center slot i believe it would work fine with only 1/32 difference in thickness. And then again maybe i am over complicating the whole thing, if the offset doesn't really matter. Please let me know your thoughts on this, THANK YOU.
Thumbnail of the uploaded file named new picture of pivot shoe.jpg
A handy person from mo says:
Looking thru your website i found pivot shoe 15-046, it has the slot centered in the top of the pivot shoe to accept the end of the spiral balance, but it is 1/2 thick instead of 17/32. do you think this shoe would work with the 900 series spiral balances? And would the 1/32 difference in thickness matter that much? Again just a thought, please let me know your opinion, thank you.
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Paul from SWISCO responded:

Personally I have never experienced the angle slot to be an issue when it comes to installing a tilt balance. I actually prefer the slot towards the outside.

As for using the 15-046 pivot shoe, you may have enough play in the track for it and you are also able to use the center slot.

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