what does this do?

[livinblokey]

Removed drive shaft to replace split cv boot today, then decided to remove other side aswell as they are all perished and replace all four. Then got carried away further and removed all of the rear wishbones to take to work to get sandblasted and refurbished(perks of the job).Anyway back to the point, does anyone know what purpose the threaded bolt has that is almost touching the cog on the diff?

[HRG.]

That's the sender for your speedo.

[livinblokey]

you live and learn! cheers