.028. If you buy Bosch Super plugs, they're set to that at the factory. Check them before you put them in just in case they get thrown out in shipping, but I haven't received one yet that wasn't right.
.028"
The suggested spark plug gap for a 1973 Harley Davidson is 0.040. It is the suggested gap for most of the spark plugs of that era.
.024
.040
( .035 inch ) spark plug gap for a 1973 Dodge 318 V8 engine , according to my Chilton book
.040
.035 inch spark plug gap for a 390 V8 in a 1973 Ford truck ( according to www . motorcraft . com - no spaces )
0.020 for the points gap, spark plug gap 0.028 -0.033
for the NGK plug # 2411 it calls for a gap of .032
Between 0.025 and 0.028 is recommended.
.044
.035 inch