Balls are used with Seats (APLA-92926), and O-Rings (APLA-9452K91) Balls sold as 4 Pack.
All Apla-Tech Jr. Pump require four Balls. When rebuilding/replacing your Jr. Pump Balls and Seats, we recommend purchasing:
(1) Balls 4 Pack,
(2) Seat 2 Packs,
(4) O-Rings for Seats
Or simply order the Apla-Tech Pump Balls & Seats Rebuild Kit (APLA-JRPUMPBSKIT) which includes everything you need.