We make our parts to a very small tolerance and the Telescope Manufactures may have made some changes over the years.
Warm up the Big Knob or Big Wheel (sunshine for 5 minutes) BEFORE you try to install. When installed it will cool off and result in a very good fit.
Please note the smooth side (by touch or feel) of the Single Big Knob faces toward the telescope. Two Step knobs the large knob faces toward the telescope.