Sometime back, I did encounter a pair of Speedplay pedals that fit entirely too snug after a couple of turns. Not wanting to risk damage to vintage Campy cranks, I retreated, and measured the OD of the pedal threads.... right at 0.5625 inches. Entirely too big by almost two thousandths. I called Speedplay, they scoffed at my notion of over-sized axles, so I mailed the pedals in and eventually got replacements!
So try some different pedals....