would depend on what motor and HP - Briggs & Stratton? check the number on the spark plug and see what the standard gap is for that plug. Most all plugs are pre-gapped when you buy them. But most small Briggs & Stratton plugs are gapped at 30 thousands ( 0.030 )
Is a The 5.6 HP
.030
Spray some ether in the carb. If it fires, it has spark, but not getting fuel. start there.
Champion RDJ7Y is the correct number.
.030" Champion RJ19LM or J19LM for manual, go to: http://www.disruptit.com/manuals/L0020135.pdf
.03
.30 gap for craftsman 3.5
0.030"
Rj19lm or j19lm
According to Craftsman owner manual for 4.75 horsepower mower model 917.388920 spark plug RJ19LM the gap is .030. Also: Oil type (API SG-SL) SAE 30 (above 32 F) and SAE SW-30 (below) 32 deq. F Blade bolt torque 35-40 lbs.
Spark Plug gap is .025
Not sure how to answer your question with the right answer. However, lawn mower spark plugs come in three sizes: 5/8, 3/4 and 13/16.
The Briggs and Stratton part number for a standard spark plug is 496018S. You can either buy this exact plug or call around to local lawn mower shops or auto parts providers (NAPA, O'reilly's...) and get them to cross reference the part number to see what other plugs will work.