This is the 2013 version of the 1 BTC brass coin. It is the most common Casascius coin when not accounting for the DIY aluminum rounds. 2014 versions of this coin would have surely been even more numerous, had Casascius not ended the sale of pre-funded coins.
This coin was the first to have a ‘lobe’ cut into the private key pit in order to help stabilize the private key and first-bits during assembly, as they often appeared crooked in older coins.
Some Casascius coins, including up to about 100 1 BTC coins, were funded in 2015 and 2016. They had been originally sold by Casascius to re-sellers during the period of normal operations, who had paid in full with the agreement that funding would happen at a later date when the reseller sold the coins. As far as it is known, all such coins are now funded, with ~36 being
in 2015 and ~75 in 2016. It is not known what amount of these late-funded (LF) 1 BTC coins were brass as opposed to silver, but many of those that were latefunded are likely to be this variety.