This is in fact a manhole cover key. The T shape is to have a grip to pull the manhole cover off. - eBay
This key has a 'Buy-it-Now' Price of $150 and an opening bid of $50 (Plus $4 Shipping) but did not attract any bids.
It has been relisted here with an opening bid of $39 and a 'Buy-it-Now' price of $60.