Dome Light Mounting Bracket. Made by the US Army Tank Command, p/n 10917855. NSN 6220-00-840-9528. Original application is the M113 Pershing, Could be used on other applications, such as trailers, agricultural equipment,hot rods, commercial trucks. Measures approx 5-1/2″ O.D. More Specs below. C/O:1-PLATE oa od 5.500 in., oa ID3.937 IN.0.0523-0.700 in.thk, 4-HOLES 0.190 in.dia 3.187 in.equally spaced, 2-STUD P/N10917855-2, oa LG.1.250 in., od 0.250 in., matl for plate;steel carbon, 1008 thru 1020, hr po or cr, temper NO.2 thru 5, quality, finish and edge classification opt., spec QQ-S-698;MATL for stud, steel carbon, 1015 thru 1025, cf or cd spec QQ-S-634 15120 L3C6+T3RA?