I'm going to be building a cnc machine with a 276oz/in stepper with a 6.35mm (1/4") shaft on the X axis. The total run of that axis will be about 30 inches. I am going to have a tensioner/idler that will keep the belt fairly tight, but I want to use something wider than the 6mm GT2. I'm not married to the GT2 profile either. I'd really like to pulley and belt that was 12mm or more wide that will mount to this shaft.

I could use a lead screw but don't really want to spend the money on that.

Thanks.

GT2-5mm has up to 15mm wide belts.

Since you're doing a belt drive, I assume you've read through this thread:

Stock Drive Products. sdp/si.com.