This is a thumb rest/finger rest for bass guitars. I use one myself. (It's removable, so I sometimes take it off when I'm mainly playing with a pick, but I usually keep it on.) For fingerstyle bassists, the thumb placement is a constant topic of experimentation, you could even say it's an eternal theme. (The tone changes depending on whether you play closer to the bridge or the neck, and also the position where you pluck the strings.) This is the stick-on type for those who don't want to drill holes in their precious bass. Images 1 and 2 show it actually attached to my bass. It attaches with double-sided tape. I recommend strong 3M tape, which you can find at home improvement stores, but other types will work too. Refer to the images for dimensions. Thickness is about 4mm. I only use two, but this is a set of three. The thickness is just right for me, but if you prefer a narrower width or want more thickness, you can stack them. If you have any questions, please ask in the comments section. Please see my past ratings for reliability. Thank you. Color: Black *White is also available (If you want white, please let me know in the message section before or immediately after purchase.) Search keywords: finger ramp, finger rest