Polaris C-500 Tinned Copper Splice- Long Barrel, 500 Mcm
https://nsiindustries.com/product/polaris-c-500-tinned-copper-splice-long-barrel-500-mcm/
Splicing conductors are the professional’s choice for making quick in-line connections and repairing damaged wiring. Use POLARIS splice connectors for bonding solid or fine stranded UL-listed wires in harsh environments.