HorACE Bow Guide for cello bow practice, a correction device for 4/4 to 3/4 size cellos. By attaching the HorACE Bow Guide to the cello and playing while moving the bow along the guide, this practice tool helps you naturally learn the correct bow technique. - Brand: HorACE - Model Name: BG-340 - Type: Bow Guide - Material: Plastic I bought this because I wanted to try it out, but I'm not using it, so I'm selling it. I thought it was something to use when you're just starting to learn and before playing songs. There is a small chip in the plastic from when I purchased it, but it is still usable. (See image 4. Images 2 and 3 show it attached to my instrument.)