I need some help for replacement of the bolt that holds the clutch plate onto the front of the air-conditioner compressor on a D2 TD5.

It seems that sometime (days, weeks??) ago I have lost the bolt that holds the clutch plate onto the front of the air-con compressor. (The weather has been cool in the last week so we may not have noticed it not working.) On the weekend when going down a steep hill, it appears the clutch plate has slid off the end of the splined shaft and into the fan, where it bounced around for half a second before being flicked up to rest on top of the engine which is where I found it yesterday!! (You can be lucky sometimes.)

Does anyone know what size bolt goes through the centre of the plate and into the compressor shaft? I suspect it is a M6 bolt but would like to confirm the correct length. Are there any tricks to getting the correct bolt torque, as it appears that the compressor shaft spins when you try to tighten the bolt. I assume it has a spring washer under the bolt head.

Thanks in anticipation.