Metric or Empirical threads on studs and bolts on Skywatcher 250P Reflector

[Cairngorm]

Re Skywatcher 250P Reflector. Can anyone tell me if the bolts/studs that attach the the dovetail plate to the tube rings are metric or imperial

Want to add a stud and rubber washer to one of the spare holes on underside of dovetail to act as a stop so as to easily mount scope in same position each time on Vixen Mount.

Gerry

[roundycat]

I think the question should be metric or imperial :-) If a modern scope and not American it is almost certainly metric.

Dennis

[Cairngorm]

Thanks Denis

Alson realised that the holes in question on the dovetail are smaller than those that hold the bolts for the Tube Rings, look about 4mm ?

Gerry

[Cairngorm]

Will take dovetail over to DIY Megastore and troll through Nut and Bolt section.

[Milamber]

I'd be worried at 4mm. Likely they are either M6 or 1/4 UNC.

Arthur

[Andrew*]

aren't the dovetail ones standard tripod fitting - i.e. the notoriously difficult to find 1/4" whitworth?

[Cairngorm]

Hello Arthur.

Realised Tube ring bolts and holes at farthest ends of dovetail are bigger.

Bolt will be placed in extra available smaller hole about six inches along dovetail base, together with a thick rubber washer. When scope is placed on Vixen mount head I will slide the dovetail/scope down till the bolt and washer only act as a stop against the egde of the mount head/clamp so that the scope is mounted in the same posion every time.

I have another reflector that has the proper Vixen cut-out type plate which acts as a stop. But Skywatcher needs lots of effort and balance to hold the weight and screw the clamp on as well without the hole thing sliding under it's own weight.

Gerry

Thanks Gerry

[Cairngorm]

Yes they do seem to have a different thread pattern from other studs I've scoured out the old tool box, could that be Whitworth ?

Told that an Ironmonger in Glasgow can make up most anything if you have an original. Gerry

[Milamber]

Difference with Whitworth and UNC is the 55 and 60 (in that order) degree angle of the thread. Not something you'd notice by eye usually... well I wouldn't - and for our purposes the angle mismatch is insignificant.

Arthur

[barkis]

I thought Whitworth was a dead and buried thread. The last time I encountered the type, was on Battery post terminals at work.

I had a 1/4 Whit spanner for the nuts. We moved a load of batteries way back then:D Of course my latest involvement came with my LX90, when I need to make a mirror lock. The hole in the mirror cell is ??????? yes... 1/4 Whitworh.

My local hardware suppliers had a length of threaded rod in stock. And the nuts too.

Apologies for the slight drift off the topic Cairngorm.

Ron.

[Cairngorm]

Bolt from dovetail fits tripod hole on my Nikon camera so 1/4". Also quick release clamp on Velbon tripod used with birding scope has 1/4" nut and that screws smoothly into dovetail holes.

Gerry

[The Warthog]

I can go to the local Home Depot and come home with a pocket full of ¼-20 threaded screws any day of the week. Should I send a care package?

[RobH]

We have an excellent old-fashioned store here in Weymouth that has metric, UNC, UNF and Whitworth.

If you want I can pick you up what you need.

Cheers

Rob

[ringz]

Wilkinson's also have 1/4 20tpi nuts and bolt, at least they did here in Coventry last week. I'm not too sure if they were Whitworth or UNC though.

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Martyn

[The Warthog]

That explains it! All the imperial stuff is being sent to Coventry.

[ringz]

Not the Roundheads Warthog, just the Cavalier ones.

--

Martyn

[Rusty Strings]

I recently built a dob mount for my 200p using the tube rings and I can confirm the threads are 1/4 whitworth

John

[PhillyDee]

Thats just it, the proper threads are actually 1/4" x 20 UNC. As stated before ,the only difference is the angle of the theads. They will fit together, but are not the 'proper thread'.

Standard tripod/camera/telescope mounts are the UNC ones.

That explains it! All the imperial stuff is being sent to Coventry.