The SpinOlution 4oz bobbin is crafted from durable Baltic birch with a built-in clip that holds your leader thread securely, making it quick and easy to start a new bobbin. The magnetic locking system holds the bobbin in place against the flyer rod, so changing bobbins mid-spin is fast and friction-free. Compatibility The 4oz bobbin fits any SpinOlution wheel that uses a 4oz flyer: SpinOlution Pollywog SpinOlution Echo (with 4oz flyer) SpinOlution Queen Bee All 4oz bobbins use a fixed 1/4 In shaft diameter, so no measuring is required for this size. Specifications Capacity: 4oz (approximately 113g of yarn) Material: Baltic birch Shaft diameter: 1/4 In Magnetic bobbin locking system Built-in leader thread clip Personalize with Engraving Add Wildflowers or Honeycomb engraving to this bobbin through the SpinOlution Bobbin Engraving option. About SpinOlution SpinOlution spinning wheels and accessories are designed and crafted in the USA. Browse the full SpinOlution Bobbins collection for additional capacities from 4oz to 64oz.