It probably is a 5/8"
So a 5/8" flare cap from Home Depot is under $5.00
IIRC the thread pitch is 1.5
You plan on wrapping that header?
133whp-126ftlbsTQ Eclipse CD8443,Eclipse PA5422, JBL GTO751EZ, PPI 356cs(Rebranded A/D/S 346cs), JBL p1024, SubThump enclosure, RAAmat BXT, Damplifier Pro
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