Vixen GP mount - thread sizes sought

[davidrandell]

Hi everybody,

I have a old green livery Vixen GP mount, There are two screws in the top of the mount that are used to secure a dovetail bar, one of these (angled at 45deg) is a small safety screw, the other larger one is the main one used to secure the scope. Does anyone know the thread sizes of these screws?  Related to this, the smaller safety screw when fully screwed in falls short of the surface of the dovetail bar I am using, so is effectively useless here. I was wondering if anyone else has this problem and what they did to rectify it (other than getting a longer replacement screw).

Many thanks,
David Randell

[spaceboy]

Take the screws out and measure the width with a ruler. The size then relates to a metric thread. IE if it's 5mm it will be an M5 screw. You will find the 45° one has snapped at some point as this is common. Simply measure width then the desired length so that it will make contact with the dovetail in future. Once you have your sizes do a search on ebay .....simplz

[davidrandell]

10 hours ago, spaceboy said:

Take the screws out and measure the width with a ruler. The size then relates to a metric thread. IE if it's 5mm it will be an M5 screw. You will find the 45° one has snapped at some point as this is common. Simply measure width then the desired length so that it will make contact with the dovetail in future. Once you have your sizes do a search on ebay .....simplz

Thanks for the tip about measuring the diameter in mm to get the M-size. The smaller screw is an M4, ~16mm in length but looking at the screw its domed on the end so most likely has not snapped in use. I think I need a 25mm length screw - plenty out there, as you said. The problem is that the (original) Vixen dovetail bar I used has one side angled at 90deg (so effectively half a dovetail in section) but the bar I use now is symmetrical in section, and the smaller screw length is not enough to make up the increased gap formed.

[dweller25]

I have the same mount and insert a thin strip af aluminium between the dovetail and the head of the mount before tightening up the two securing bolts. This also stops the bolts damaging the dovetail bar on the OTA. 

 

 

[davidrandell]

An even simpler solution! Thanks.