L'MS Violin Bow Straighten Collimator Tool for Beginner Training Exercise (Fit for 4/4,3/4,1/2) Compatible with all 4/4,3/4,1/2 size violin Easy to install and disassemble with adjustable Velcro straps Encourages straight bowing and correct wrist action,the best helper for beginners Portable and easy storage into any violin case Great confidence builder for the student Violinist or for the seasoned player who wants to improve their bowing action