It seems to be T2 OM to 40mm reverse ring. Not sure who and how they used, But here it is for sale.

Ring thread size is 40mm, and the other side has T2 to OM adapter (it is removable, since T2 adapter has female threads). 

Shipping is free within USA and $7 worldwide via USPS first class mail service.  

It will be shipped without any accessories. Just an adapter. 

No other accessories will be included in this sale.