Mystery nut - mystery to me anyway

[NCriding]

This nut with a winged flange came with my 1936 VLD bit-sa project, the head is 11/16"

Can anyone tell me what it does, and what the part number is?

IMG_0490[1257].jpg

[larry]

Front motor mount, under the generator, Big Twin.

[len dowe]

A special lock washer goes with the bolt.

[Rubone]

The nut drops into the case from above, the tab keeps it from turning. As stated, the bolt has a special retaining washer so once it is tight the washer is bent up to lock it in place.

[NCriding]

Gentlemen, thank you for the responses!

Is this nut supposed to fit into a recessed bolt hole in the case? If so, the case was never drilled/machined for it.
IMG_0496[1283].jpg
Per the picture, I did insert and tighten the nut, without that retaining washer (I don't have one). If it had a washer [U]under[U]it, the top of the nut would be high enough to contact the generator.
IMG_0492[1281].jpg
Here you can see that wear ring, why not just use the same bolt, washer, castle nut with cotter pin as the other 3 holes? The cotter pin might be a trick to get in, but with forceps I'm sure I could manage.
IMG_0495[1282].jpg

[Rubone]

The nut was a new for '36 part and not likely used on a VL, just the new 36 OHV.

[Sargehere]

And the UL beginning in 1937, with no washer. The hole was designed to keep the triangular flange on the nut
from turning at all.

[NCriding]

Thanks Sarge, now it goes in the spare parts bin