Do I need to install a fuse on a altenator wire?

What I have now would be 2- 10 gauge wires in parallel The stock wire have a replaced fuse link out of the block, the new wire. The alt is the stock style with the 2 field terminals.
Would have a 4" of a fusible link, 12 gauge or maybe a 50 amp circuit breaker?
This is just my thoughts now, I am exploring the forums thoughts.
The picture is, I do not know what the strap is for