M939 Front Axle seal housing

[M35A2-AZ]

I am trying to replace the front axle seal on my M936 and I pulled the old housing out (that was a job!!!) and now I am trying to install the new one.

My question is on the back of the seal housing their is a key looking thing, is it important how the key faces?
To the front, back, top or bottom? Also what is the key for?
Their is no slot in the axle housing for it.

 

[rrrr]

I just replaced mine and put the key on top. I think the seal works on mulitiple vehicles. Our 5 tons don't have the indent for the key.

 

[M35A2-AZ]

Thanks for the info.