Hangar 9 Piper J-3 Cub 40 ARF - Manual (Page 27)

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 Step 5
Drill 1/16" holes through the cowl and into the fuselage
sides at the locations marked in the last step. Enlarge the
holes in the cowl using a 5/64" drill bit. Secure the cowl
to the fuselage using four #2 x 3/8" screws.
 Step 6
Attach the propeller following the instructions provided
with your particular engine.
Section 8: Cowling Installation