I always replace broken V-belts with GATES "PowerRated" belts.
The part numbers for the GATES "PowerRated" belts are:
1) For 3/8" (3L) width belts: 67XX, where XX is the length of the O.D. in inches.
2) For 1/2" (4L) width belts: 68XX, where XX is the length of the O.D. in inches.
3) For 5/8" (5L) width belts: 69XX, where XX is the length of the O.D. in inches.
O.D.: Outside diameter (in steps of one full inch, no half inch available).
For 1/4" belts you can use GATES "Truflex" belt part number 2LXXY where XX is the O.D. in inches and Y is in 1/10 of and inch.
In order to find the O.D. you can:
1) Measure your current belt.
2) Find it on: http://outdoorpowerinfo.com/
3) Find it on: http://www.gates.com/part_locator/index.cfm?location_id=3598 in the "Lawn & Garden Equipment" category.
4) Find a part interchange on: http://www.gates.com/part_interchange/index.cfm?location_id=3286
Hope this helps.
/Snow Storm