What does "bolt circle" refer to?

[RayCo]

Hi.

In a description of a tractor engine, such as this one, Honda V-Twin Horizontal OHV Engine with Electric Start — 670cc, GX Series, 1 1/8in. x 3.54in. Shaft, Model# GX670RTDW | 670cc | Northern Tool + Equipment
the specs indicate that has a bolt circle of 5, 6.5, 7.75. Can anyone tell me what this is a measurement of? What is this "bolt circle" spec?


Thank you

 

[Willl]

It's the circular mount pattern on output side of the block.

(tagged in red)

 

[banjodunn]

G'day it is also known as pitch circle diameter ( PCD )


Jon

 

[RayCo]

Got it, cool. Thank you both.