This is marked "Parabeam Headlamp, For Use With 21 C.P. Two Filament Bulbs, Pat Pend, 9 31/32 x 8 15/16, Made in USA, I.G.C., R.I."

This is 9 31/32" in diameter overall with a prism diameter of 8 15/16".  There is a notch at 180 degrees. 

According to my old catalog, this is OEM for use on:

· BROCKWAY TRUCKS  (1927-29: some used this lens and some used other lenses)

· CHECKER CABS  (1928-29: some used this lens and some used other lenses)

· EL CAR  (1928-29: Models 8-82 and 8-78)

· FRANKLIN  (1928-29: some used this lens and some used other lenses)

· HUDSON  (1927-29: some used this lens and some used other lenses)

· LOCOMOBILE  (1928-29: Models 8-70 and 8-80)

· MOON  (1928-30: Models 6-72 and 6-69)

· VELIE  (1928: Models 50, 66, 77, and 88)

There are no chips or cracks.  The lower third of the lens has a light brown stain and there is a whitch splotchy stain you can see in the last photo.  I tried removing these stains with soap and water but they still remain. 

car auto automobile automotive classic antique 1927 1928 1929 1930 27 28 29 30 commercial delivery utility pickup pick-up light lamp lighting