Top quality, made by MRB. UK made lower steering race for the forks. This race is fitted onto your forks (Series 1,2,3). They often get pitted with rust over the years so need replacing. 
 
To remove the old one use the two holes under your forks and hit the race with a drift to remove it. 
 
To fit use a soft drip and tap down on opposite sides, if it locks up, remove it and gently run a file around the fork stem (PLEASE NOTE: fork stems vary in size, some are tight some are a perfect fit, if you hit it down and it locks and you keep going the race may split!)