Which one is correct?

What's that? What are you trying to convey?

The first. 'half' is an adjective here, which don't come in a plural form. Note, there is also the noun 'half' with a plural 'halves'.

IMDJSix half hides / Six halves hide

Well, both can be correct in context.

The farmer slaughtered six of his cows; their skins were tanned into cow hides. Six half hides were sold at the market at a good profit.

There were six apples cut in half. Six halves hide under a bowl. The other six halves were eaten immediate

"Six halves hide under a bowl" Sharp.

We were supposed to receive six full cow hides (animal skin), but we only received six half hides

That's correct, IMDJ.