B21 block heater plug

[jsec]

I would like to install a block heater in my B21 when I go up there this weekend. The plug in the block that has to be removed has a fermale hex drive like for a large allen wrench. Does anyone know what size it is? I forgot to measure it last time I was up there.

 

[mrennie]

I believe it is 17 mm. I installed a block heater in my B26 last November (same block heater kit) and going by memory that was the size I used.