Mounting My PST

[David Smith]

I want to be able to mount my PST on my Celestron CG4 mount so that I can do white light and Ha on the same mount. I have a skywatcher dovetail and notice the mounting bolts for my old short dovetail fit perfectly in the pre-drilled holes but are not long enough to reach to PST thread.

These are stated as 0.25" whitworth fasteners but my search of various websites has failed to find such an item. Does anyone know if I can just by a longer bolt that will capture the PST thread through the dovetail and if so what are they called.

Appreciate your help

Thanks

[Gina]

Whitworth threads are near enough UNC to work fine and there's no shortage of UNC screws on the ol' well known auction site

[StarlightKnight]

David

Scope Teknix stuff doesn't seem to be available anymore.

I'm not sure if you can get any longer bolts but faced with a similar problem I ordered a Vixen style photo dovetail from Bern at Modern Ast... yesterday.

Don

[JamesF]

I thought they were in fact 1/4" UNC as fitted to camera tripods.  I can't recall if I ever put mine on a camera tripod to check though.

James

[Peter Drew]

Camera tripod fixings always used to be either 1/4" or 3/8" BSW. The equivalent UNC has the same pitch but the included thread angle of the UNC is 60 degrees and that of BSW 55 degrees. The UNC screws as a result can sometimes be a little tight when used in a BSW fitting.     

[JamesF]

Camera tripod fixings always used to be either 1/4" or 3/8" BSW. The equivalent UNC has the same pitch but the included thread angle of the UNC is 60 degrees and that of BSW 55 degrees. The UNC screws as a result can sometimes be a little tight when used in a BSW fitting.     

Aha!  There appears to be chapter and verse here: http://en.wikipedia.org/wiki/Tripod_(photography)#Screw_thread

James

[David Smith]

Thanks to all for your replies. I have ordered a couple of different length 0.25" UNC hex cap bolts. At a total cost of £2.30 I am not too worried if they urn out to be not what I wanted but sounds like I am on the right track.

[David Smith]

Just for the record (in case anyone looks at this thread later) I recieved

one of 0.25" x 7/8" UNC Hex cap bolt

one of 0.25" x 1" Hex cap bolt

this morning. Both fit the PST and screw into the pre-drilled holes in my Skywatcher long dovetail. I have yet to try actually attaching the two together as I am short of time this morning but both look long enough to do the trick.

Thanks again for your input