Steve,
yes that's the bit.
I'm no expert but talking to the guy, it's the bit that rests the bell when it is pulled just over the vertical. There is a second component to it that moved backwards and forwards (the slider in your image) on a pivot at the opposite end, so the bell can be rested from either side.
He says they sometimes break if it's rolled a bit hard, but much more so if it's air dried timber. There can be a couple of tons of Bell resting on it.
Actually that part is only a roughly planed section of timber, no turning involved, but it's because of this part, he wants air dried timber, not kiln dried.
I was surprised to find out just how many turned parts there are up in a belfry.