It's all about what position the clip is in when you're trying to get it out. If the clip is on the top of the shaft and hanging down so most of the clip is in the groove, they pop out easy. But if the clip is hanging off the bottom, then there's a lot of material sticking out of the groove that holds the axle in place and takes a lot of force to remove. So if you're ever trying to remove an axle and its being stubborn, push it in and rotate it 180 degrees and try again.