This is the HorACE Bow Guide, a corrective device for practicing violin bow strokes. I've used it for about six months. Please understand that this is a used item. The actual product is shown in the fifth photo. The following is a quote: The guide part is made of lightweight and durable polycarbonate resin, weighing only about 26 grams (for 4/4 to 1/2 size violins). When practicing the violin, you might be surprised at how difficult it is to move the bow straight. When you're focused on fingering with your left hand, doesn't the angle of the bow sometimes go awry, or are you playing on the fingerboard or the bridge? Almost all beginners constantly have these concerns. To play with a beautiful tone, you need to move the bow in the correct position and at the correct angle. This HorACE Bow Guide is a practice tool that you attach to the violin as shown in the photo and use to practice playing while moving the bow along the guide. The legs are made of flexible silicone material. Gently squeeze the legs with your thumb and index finger, slightly reducing the distance between them. Then, release your fingers so that the concave part of the legs touches the C-curve edge of the body of the top plate. It's that simple, so there's almost no risk of damaging the violin when attaching it. Removing it is also a simple process. The ease of attachment and detachment greatly affects motivation during daily practice. As mentioned above, this is an excellent bowing practice guide. Please give it a try.