If you do get the Butler Creek covers, go on the Vortex site and look at the specs for your scope, it will give you the exact dimension for both ends.
Then look at this table and choose the model accordingly:
http://www.butlercreek.com/productsImages/charts/flip_scope_chart.html
*warning* the eyepiece and objective lenses are both numbered 1, 2, etc but the models refer to different sizes. This causes huge confusion with Butler Creek covers.
Edit: Also, my PST 6-24 has a soft rubber end on the eyepiece, the Butler Creek cover did go on but I was afraid of damaging the rubber (vs metal focus ring).