Harmonic Balancer Bolt, Hex Head Black Oxide AR135-2503Harmonic Balancer Bolt, Hex Head Black Oxidefits BB Chev 1 2 20 Thread x 1. 550" UHL With 1 2" Square Drive AR135 2503 135 2503 Arp Offers A Special Version O f Its Rugged Balancer 200,000 Psi Rated Balancer Bolt That C an Accept Standard 1 2 Drive R atchet Or Breaker Bar To Facil itate Rotation Of The Crank As sembly. * 1 2 Square Dr ive Forged Into Bolt Head, Ena bling The Rotation Of An Engin e With Any 1 2 Drive Tool < br>* Made From Heat treated