Window Channel Balance 29C Replacement

Dear Sir Or Madam,

I need to replace 6 channel balances. The old ones are 29C (marked on them). They look like your "29" Series 770 Balance". The problem is their depth - it is not 5/8in as I've been able to find in a number of places, but exactly 1/2in. 5/8 will not work. Are your balances 5/8 in deep or 1/2 in. If the 1/2 ones come at a different cost, what would the cost be?

Thank you,
Dan