The auxilliary battery tray contrains a threaded hole to which you can bolt a battery hold down bracket to. It lines up perfect with the bracket supplied with Optima batteries. Can someone tell me what thread size it is? I suspect it's metric.

 

It is probably 8 X 1.25 or 10 x 1.5

 

I think you can pick them up at Auto zone or pep boys as a complete assembly the mounting block and the bolt included, probably find it on the isle with the replacement goodies. If I were to take a guess I would have thought 1/4-20

 

1/4-20 is old school. Just about everything, especially body/chassis, is metric. I hate it. But good excuse to buy more tools. Not to mention stocking up more fastener assortments.

 

For the record, it took 2 trips to Home Depot to determine that it's a M8x1.25 hole and it's made to clamp the bottom of a BCI Group 34/78 battery.

 

I just wished they had left metric on the other side of the pond.

 

You go hardin, I was jacking with that a bit this week also, I was trying to check it with a tap and die set I had but my set didn't have all the metric sizes.....