These are a set for both the front and rear timing chain tensioners.
The reason is mysterious but it seems one of the first things to give any trouble on Vulcan 1500/1600 engines is the cam chain tensioner. That's the spring loaded tensioner that keeps an idler pressed against the chain so it doesn't whip or come off the sprocket or even make nasty grinding noises as it stretches through normal use.
At some point though the tensioner reaches the end of its travel and then, when the chain stretches just a little more it starts rattling, usually against the spark plug tunnels (tubes) causing the damage. The chain can eventually wear a hole in those tunnels which then fill (slowly) with oil and suddenly the rider notices oil seeping down the side of one cylinder.