The sky is the limit with these 2.5" Spin Wheels! With a 1/4" inner hole and 1/4" triangle outer holes, these parts come ready to use. Imagine the possibilities! They are currently available in Red, Yellow, Green, Blue and White. Recommended sizing: small to large birds. Recommended stringing material: Polly Rope, 1/8" leather laces and 1/4" Supreme Cotton Rope™ (with a little effort) .