Mystery bolt leftover after installing waterpump descrip 12MMhead M8-1x40mmthrea

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1987 nissan z-24 pickup Can you please tell me where I need to put this Mystery bolt that is leftover after installing a new waterpump description of the bolt is a 12MM head M8-1.0 x40 MM threads and it has a lockwasher on it and there is a number 7 on the head. I think it is an original bolt. There was no nut left in my box I was putting the parts I took off in so I think it goes into a threaded hole somewhere.