Spinnaker block

[Pili Aloha]

I have a Hunter 45 CC with no block for my spinnaker. I would like to know a safe working load for a block with 3/8" line before I order a new block.

 

[markwbird]

There are a number of blocks used in the rigging of a spinnaker: Topping lift, foreguy, turn blocks, halyard.

 

[DArcy]

Try the Harken Genoa calculator Harken Sailboat Hardware and Accessories
I know you are asking about spinnaker but the loads will be similar and it will give you a good idea of approximate loads. If you poke around on their site you may find better information.