Ignition Coil 6 Volt Twin Lead. Universal fitment, so can be used on those old American bikes, but also the Japanese or English motorcycles should work fine with it!

Twin Lead Ignition Coil 6V.
The HT Leads are 23-1/2"(590 mm) long.
Mounting bolts are 3-9/16" (90 mm) from centre to centre.

Black lead: Negative
Yellow lead: Positive
Primary resistance: 1.09 ohms
Secondary resistance: 13-14 ohms.