Explorer 150 collimation Allen screw size ?

[haroonxml]

Can someone please guide me on this or if you have any links from where I can buy these as I have tried a few and none of them fit.

[Moonshane]

I'd have thought m4 or m5, standard threads. I'd replace with thumbscrews personally.

[haroonxml]

Can someone please guide me on this or if you have any links from where I can buy these as I have tried a few and none of them fit.

Sorry I should have mentioned that I am talking about the ones that are used to collimate the secondary mirror. 

[NGC 1502]

Chances are high that metric allen keys will fit.  If you get a half decent set  (choose a set with lots of the smaller ones)  you should find one that fits.

Hope you sort it, Ed.

[JB80]

I ended up buying one of those cheap sets on a ring with about 20 different sizes for mine.

One of them definitely fits but as to which size it is I don't know, one of the small ones anyway.

[bambuko]

Appears to be 2mm allen key for M4 grub screw on mine.

[astronymonkey]

id still replace with thumbscrews as this reduces the risk of dropping an allen key down the tube onto the primary 

[bambuko]

Alternatively... only use allen key with the tube pointing below horizontal (ie downwards)

[Moonshane]

sorry I misread this completely. I thought you were asking about the screws not the keys. yes, a standard metric set would have one to fit, I think it's 2mm.

[Roger Fairhurst]

It is 2mm

I found that mine were very tight indeed although I was using the type of Allen Key with a "ball" end. It's probably better to use the cheaper, straight ended variety. You might even have to eytend the length of the key with the help of a small tube in order to get enough moment to actually turn the adjusting screws.

Also to adjust I think you need to slacken one off first and then tighten one of the others and repeat until collimated.

I'd be interested to hear how you get on!

Kind regards

Roger

[bambuko]

and then you will end up gouging secondary mirror holder

see also:

secondary holder - Skywatcher 150p