Serious bowlers using the Turbo Switch Grip system, listen up! This is a green inner sleeve (or 'slug') for your interchangeable thumb grips. The size is 1 1/4 inches. It's a core component of the system: you glue this inner sleeve permanently into your bowling ball's thumb hole, and then your various outer Switch Grip sleeves snap into it. This allows you to quickly change thumb fit and feel between balls. It's from Turbo, a trusted name in bowling grips. Brand new in its packaging. If you're setting up a new ball or replacing a worn inner sleeve, this is exactly what you need. Essential gear for any bowler who values consistency and quick adjustments during league play or tournaments.