Not sure. But....
https://www.gunpartscorp.com/products/1111360A
which is listed under
https://www.gunpartscorp.com/gun-manufacturer/taurus/revolvers-tau/66-old-model
https://www.gunpartscorp.com/products/1111360A
which is listed under
https://www.gunpartscorp.com/gun-manufacturer/taurus/revolvers-tau/66-old-model