What I am trying to do is remove the water plug on the passenger side cylinder head so that I can install an after market fan switch. According to the directions I need a 5/16 square head wrench to remove it. Do any of you who have removed this plug know where I can find such a tool? Thanks

 

I have used a piece of square bar stock from Home Depot and an open end wrench before. I couldn't find a tool anywhere.

 

Thanks