Replacement window channel width question

I'm puzzled by something that doesn't add up to me. I believe my double hung windows to be relatively standard. The two sashes are 1 3/8" thick with a 1/2" parting stop which adds up to 3 1/4 inches total. This means the distance from the blind stop to the back edge of the window stool is also 3 1/4". Replacement pocket windows seem to be 3 1/4" wide and will fit in this gap nicely. However all of the replacement window channel kits I've seen, and even the replacment sash kits are 3 1/2" wide. They won't fit unless the blind stop is removed or the stool is narrowed, neither of which should be necessary according to the manufacturers.
When I asked the guys at the local big box home supply store about this they said they've sold hundreds and have never heard this question before.
What am I missing?
Thanks, Tom
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Me too! I've tried the aluminum replacement channels and looked at a Marvin Tilt-pak channel and neither seem to fit the window channels on my 1926 home. Here's some pictures of my window channels demonstrating the problem:
http://mysite.verizon.net/nwoodmnr/windows/window_jambs.html
I need to refurbish or replace 6 remaining windows so I'll be revisiting this issue soon. Haven't talked with the window manufacturers or installers yet on how best to solve the problem though.
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Yep. This is exactly my problem and I have the same aluminum channels from Quaker Manufactuing. What puzzles me is that I think our window jamb width is "the standard" at 3 1/4" which means none of these replacment jambs fit most people's windows. I'm still hoping someone on this newslist will explain this. I thought if routing out the bottom of my sash to get the window to fit as you did, but instead, I cut the side pieces of the jambs off to narrow the width. The front and back stops hold the sashes anyway.
I'd buy Marvin Til-Pak's myself if I could get them to fit without removing the blind stop.
- Tom

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