Need channel balances for older window

A contractor from Columbia md says:
March 10, 2015
Trying to identify the proper channel balance for replacement. My current balance is stamped with 18D. So it looks like I need a 19": Series 371 seems to be closest but may not be exact. The bottom plastic piece is likely 15-005 (those measurements are the same as my existing piece), but I am having trouble identifying the top plastic piece. 19-031 doesn't match my existing piece exactly. My top piece is 15/16" wide and the tabs are 3/8" tall.

Thanks for any help,
Mitch
User submitted photos of a window balance.
Profile picture of Paul
Paul from SWISCO responded:
March 13, 2015
Thanks for posting! There's a good method of confirming whether our Series 371 can work for you or not. Take a look at your top sash guides. If they look like our 18-124P, then you should be good to go. These are for Rollyson windows, which is what our Series 371 is made for.
19" Series 371 Channel Balance
19" Series 371 Channel Balance
S371-19
$9.34
Channel Balance Top, Rollyson
Channel Balance Top, Rollyson
19-031
$1.47
Winged Channel Balance Shoe, 1" Depth
Winged Channel Balance Shoe, 1" Depth
15-005
$0.74
Top Sash Guide Pair, Rollyson
Top Sash Guide Pair, Rollyson
18-124P
$3.92
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