I use a polished rubber ball from the 60's for my spares. The ball will bend a little bit on drier lanes but it's still well within my radius of error (!) for spares.
Having said that, I'm sure a plastic ball would go straighter.
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It is by Caffeine alone that I set my mind in motion. It is by the beans of Java that my thoughts acquire speed. The hands acquire shakes, the shakes become a warning. It is by Caffeine alone that I set my mind in motion.