Magnetic 'C' Channel Label Holders, 1 in.x4 in., SKU: LH-0118 Product Description. C-Channel Magnetic Card Label Holders are the best choice for metal racks and shelves. 100% magnetic material assures total adhesion in any application, while the unique C-channel lets you slide out an old label and slide in a new one in seconds. 1" x 4" Magnetic "C" Channel Label Holders. Standard product thickness is 1/16".