To provide a non-slip device not interfered with peripheral members, having high reliability, and easily manufacturable at low cost.

These connection systems 5, 60 connect a chain part 10 to the inner ring 3 of the non-slip device. The chain part 10 comprises a chain having a twisted ring 11. The connection systems 5, 60 comprise a U-bolt element 50 fitted to the inner ring 3 and a ring 60 at the end of the chain part 10. The ring 60 at the end comprises a twisted portion 61 connected to the twisted ring 11 of the chain part 10 and a flat straight portion 62 connected to the U-bolt element 50.