Size: Extra Small | Style: CP100 (bore size 4 mm / Single Flange)SpinFit is a patented ear tip. SpinFit has an ergonomic concave design at the core to allow the ear tip to swivel, making it flexible to bend and twist to the contour of a person's ear canal. SpinFit ear tip is able to be inserted deeper into the ear canal, enabling less obstruction along the sound field dispersion path, which results in greater audio experience while providing maximum comfort.WHAT SIZE? The different size ear tips accommodate to different ear canals. Choosing the proper size is critical for a secure, comfortable, and quality result. If you?re unsure, medium size fits most users comfortably. WHICH MODEL? CP 800: nozzle (core) dimension is 2 mm (Single Flange) CP 100: nozzle (core) dimension is 3.8 mm (Single Flange) CP 360: nozzle (core) dimension is 3.6 mm (Single Flange) - for True Wireless CP 155: nozzle (core) dimension is 5.5 mm (Single Flange) CP 240: nozzle (core) dimension is 4 mm (Double Flange - deeper insertion) - CP 240 using insert: nozzle (core) dimension is 3 mm COMPATIBILITY. Different models are designed with different core sizes to fit all major earphone brands.Please confirm earphone model / measurements before purchase!CP 100 series fits models including: Audio-Technica ATH-CKR10, Bose SoundSport, Jaybird Endorphin Rush, JVC HA-FX45S, Panasonic RP-HJE140, Soundmagic EH-11, Beats X, Powerbeats 1 & 2 & 3, Campfire Audio Andromeda, Jupiter, Lyra, Vega, Plantronics Voyager 855, Trinity Audio Hyperion and more. QUESTIONS? Don?t see your earphone model?Contact us and we will recommend you with the best eartip option.100% customer satisfaction guarantee.