Keystone  E-Z Clean Sliding Shower Door Bottom Guide with Hook;
Keystone Part Number MS00169
Keystone Models: 105 / 107 / 205 / 805 / 807 / 905
Sterling Had a similar design in Clear Plastic 

bottom mount Guide - Gray plastic
Width 1-1/2 inch
length: 3 inch
screw holes: 2 inches apart
Sold: Pairs (2)

Note 1: This sliding shower door bottom guide does not come with spacer - See Additional Images
Note 2: May be slightly Different than original - See Additional Images

Spacer shown in 2nd photo is no longer available. You can reuse your original spacer or place washers under to achieve the same effect.