I don't know what they are called but they can be found in the hardware department of any home improvement store. They look like links in a chain but have a piece that screws open and shut. They can be found in many different sizes. Here's one on Amazon: https://www.amazon.com/gp/product/B007HRNXP8/ref=s9_acsd_topr_hd_bw_b52RMCB_c_x_w?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=merchandised-search-10&pf_rd_r=32TY6YQWD3N0FW8JWBN9&pf_rd_t=101&pf_rd_p=761b7554-590d-5cb9-afcb-e8f319d4dc08&pf_rd_i=4616737011

But note... they will not fail. So any tooth or toenail that gets caught in them will fail before the hardware does. Just something to consider.