Hi, HandyJAB - Generally copper tubing is 1/8" larger than the ID (nominal) measurement. So your 1-1/4" ID tube would have an OD of 1-3/8" (1.375"). Doing a measurement of several samples at our main office, our tubing cutter opens to 1.40". Given the +/- variables of all types of pipes, it's possible that the walls of your copper tubing were to the high side of the specs and were just slightly larger than the overall opening of our cutter. Sorry for the inconvenience.