These nets are for standard round bales with a diameter of 140cm = 4' and come in 5 different models:

RB140 Low has a height of 155cm, cover a standard round bale from the top down or a bunch of small bales or a pile of loose hay when used as a large bag with the opening facing up.

RB140 High has a height of 220cm, takes a full standard round bale from the bottom up, which by the way is the by far, best way of dressing a round bale in a SlowFeeding net.

RB 180 Low can replace an RB 140 High but is wider and lower, but with the same net weight, to make it easier to dress a regular round bale.

FR 160 to be fitted permanently in a round bale feeder as on the picture (tip the feeder with net over the bale).

FR230 is made to cover a full standard round bale standing in a feed ring with 12 eating places. 

Your choice of mesh size doesn't affect the price.