Slackers Ninja Ball with Hardware (2 Piece), Red/Blue, 2.5" Poly Resin Top training for building forearms and grip strength Two piece ball kit includes: 2.5" poly resin textured balls (tennis ball size), with hanging steel bolt, triangle safety carabiner, and 7.5" length x 1" polyester webbing sling B4Adventure NinjaLine Premium Accessory Ages 5+; Max weight 250 lbs Endorsed by "The Ninja" Brian Arnold