I broke mine too the first time I took off my horn ring. It is called a Horn Retainer Plate and you can get a new one from LMC or another supplier for about $8. Yours was probably brittle with age (like a lot of us).
jor
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-O-----O- Keith
'67 F-100 2WD SWB ~ '69 F-100 4WD SWB w/7" chop ~ 1975 F-250 Ranger XLT Supercab Camper Special My '67 restoration video -> Posting and you!<-a MUST watch for all!!