On one of the lastest plains bows was a hole from a little branch, just where the string was meant to be sitting. This is not a drilled hole -it is natural. Instead of carving a pin nock or something else, this hole was used for the lower string fixing. Here are some pics from this unusual nock, as well as from the upper triangular shaped pin nock.
The finished bow is here
The how to of a fish skin handle on this bow is here
Now for the tips:
upper pin nock
To fix the string: use dental floss to get the ‘thick’ string through the hole, begin from the belly side of course. The string has a ‘normal’ eye.