MM replacement window tension insert rail for side of 34x29 rial length is 28" - number and marks on the rail 26 4 CMC 7

Hey there!

Thanks for reaching out to us. Take a look at the Series 380 and Series 385 channel balances. One of these may be what you need depending on the depth of the bottom fitting. You can select the 2640 stamp option for your replacements.

The metal channel should measure 27" as well. When determining length, be sure not to include the end fittings in your measurement. 

Comparison of the S378, S380 and S385 balance shoes.