Me personally, I have the span on my spare ball shortened 1/8th of an inch, to keep me from putting extra revolutions on the ball. This helps me, since I only have med. ball speed. I don't know many people that change their drillings between their spare balls and the rest of their equipment, except one other guy I bowl with who twists the ball, he doesn't use finger inserts in his spare ball (but then again, he sucks at spares)! Just my $0.02
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"I was raised by a cup of coffee..."