NOS K-D 517 Red Glass Cab Marker Light Lens
They have slightly curved bases that fit curved roofs like B Model Mack trucks. See 6th photo.
Most don't realize they are curved on bottom and are used and will work on flat roofs.
I have 3 available. All are in excellent condition, no scratches or chips except for chip on front of 1. It would be covered by bezel. See last photo. The other 2 do not have any chips. Vintage glass and they have wavy lines that are made in production.
One photo shows all 3. Listing is for 1 with the option to purchase 3.
Please see photos, confirm fit and ask any questions before purchasing.