Externally threaded to fit fixing nut. Internally threaded to fit standard Fender etc. pilot light jewels. Fits many old guitar amps. Great for restoring older Fender amps or for building 'clones'. Yes, these will fit your '50s-'70s vintage Twin Amp, Twin Reverb, Showman, Bassman, Pro Reverb, Super Reverb, Bandmaster, Champ, Vibro Champ, Deluxe, Vibrolux, Tremolux, Harvard, Princeton etc. exactly. Also fits many other vintage amps by Silvertone, Supro, Oahu, Airline, Danelectro, Ampeg, Gibson etc. I measured .681" diameter on a sample. Upper lip (the part that rests on face of the chassis...) measures .752". Collar measures .447" overall length. Brand New. Genuine Fender part 0032219049. UPC 717669612849.