Stirrup leathers go through a lot of stresses and strains so using the best quality English leather is very important. Some leathers will stretch quicker than others and that’s down to a number of factors, including how you mount and how you ride.
It’s vitally important that you regularly check your leathers for stretching.
Leathers that are uneven in length (they can stretch at different rates due to rider position) will cause problems for your horse. So I recommend that each time you take the leathers off your saddle that you compare them both. Looking at the hole number won’t give you an accurate guide, it’s best to measure them. Swapping them over from one side to side each time you clean is just one way to help keep them as even as possible and always try not to mount from the floor but from a mounting block.