The Siemens 5SJ6363-7RC is a 3-pole miniature circuit breaker (MCB) from the Retail line, rated 63 A with a C characteristic and a 6 kA breaking capacity. This is a current-production part, so it's a standard BOM line item, not a scavenger hunt.
At 63 A per pole, this breaker handles a 3-phase load up to about 35 kW at 400 VAC. The 6 kA breaking capacity (Icn per IEC 60898-1) is the maximum fault current it can safely interrupt; that's adequate for most residential and light commercial distribution boards, but verify the prospective short-circuit current at the point of installation — if your panel's fault level exceeds 6 kA, you need a higher-rated breaker upstream or a current-limiting device.