Bell Knobs .Black//Black Pearl Top ~ Pkt of 2. They get broken, they get lost, but where can you go to get the best selection of top quality replacement and retro-fit control knobs for your precious guitar or bass? Guitar Tech, that's where. Guitar Tech offers a comprehensive, attractively packaged range of precision moulded, accurately-designed control knobs, featuring clear, high quality markings, that are a direct fit for your instrument, from sleek and smooth speed knobs to knurled edge, dome cap barrel types.