Explore Scientific 9.9 Pound Counterweight for EXOS-2 and EXOS-2GT Equatorial Mounts

Product Overview

This is Explore Scientific's supplemental 9.9 pound counterweight for the EXOS-2 and EXOS-2GT equatorial mounts, item EXOS2CWB, finished in black and supplied with its own locking knob. Explore Scientific publishes the mass as 9.9 pounds, which makes it the larger of the two counterweights offered for the EXOS-2 shaft. It is the weight you add when the tube on the saddle is genuinely heavy and the counterweight you already own has run out of shaft to travel along.

Who It's For

You need this one when you have added real mass to the saddle. A 6 or 8 inch Newtonian, a 4 inch or larger apochromat in rings on a substantial dovetail, or a refractor carrying a full imaging train — camera, filter wheel, guide scope, and cabling — pushes an EXOS-2 past what a single smaller counterweight can balance. The symptom is unmistakable. You slide the existing weight all the way to the end of the shaft, tighten it, release the clutch, and the tube still drops. At that point you are not looking for finer adjustment, you are simply short of mass, and no amount of repositioning will produce it.

It is also the right choice if you would rather reach equilibrium without hanging the weight off the extreme end of the shaft. A heavier counterweight balances the same tube from a position further up, which keeps the assembly more compact, reduces the swing you feel when the clutches come loose, and leaves you shaft length in reserve for the next accessory you bolt on. If you already suspect that something large is going onto this mount eventually, buying the 9.9 pound weight first saves you buying the smaller one twice.

Key Features & Design

• Explore Scientific publishes a mass of 9.9 pounds, the larger of the two counterweights offered for the EXOS-2 shaft
• Locking knob included, so no separate hardware is needed to secure it
• Black finish matching the EXOS-2 and EXOS-2GT mount head
• Bored to slide directly onto the EXOS-2 and EXOS-2GT counterweight shaft
• Sized for heavy optical tubes and loaded imaging trains rather than fine trimming
• Stacks with a second counterweight on the same shaft when total load demands it
• Supplied as Explore Scientific item EXOS2CWB

Mechanical Design

Balancing an equatorial mount is a question of torque rather than weight. The turning moment on either side of the right ascension axis is mass multiplied by its distance from that axis, so a counterweight of a given mass can balance a wide range of tubes depending purely on where it sits along the shaft. What the shaft length does is impose a hard ceiling: once the weight is at the far end you have extracted every bit of leverage available and the only remaining variable is mass. At 9.9 pounds this counterweight produces roughly double the moment a five pound weight generates from the same shaft position, which is why it is the answer to a heavy tube rather than an awkward one. There is a second benefit that is easy to overlook. Because a heavier weight balances the same load from closer to the mount head, it draws the centre of mass of the whole rotating assembly in toward the polar axis. That lowers the moment of inertia the drive has to accelerate on every slew and reduces the pendulum effect when the clutches are released, both of which make the mount calmer to work with.

Recommended Uses

• Balancing a 6 or 8 inch Newtonian on an EXOS-2 or EXOS-2GT
• Balancing a large apochromatic refractor carrying a camera, filter wheel, and guide scope
• Adding capacity when your existing weight is already at the end of the shaft and the tube still drops
• Replacing a lost or damaged original counterweight
• Stacking with a second weight for the heaviest loads the mount will carry

Compatibility and Accessory Notes

Explore Scientific specifies this counterweight for the EXOS-2 and EXOS-2GT, and it is the direct match for the counterweight shaft fitted to those mounts. It arrives with its own locking knob, so it can go straight onto the shaft alongside a weight you already own and the two will stack without extra hardware. Before ordering, check the free shaft length below your current counterweight, because a 9.9 pound weight occupies noticeably more of it than a smaller one and a shaft that is already crowded may not accept both. Remember too that counterweight mass does not raise the mount's rated payload — it only lets you balance what is already there — so if the tube itself is near the EXOS-2 limit, more counterweight is not the fix. Explore Scientific does not publish the bore diameter, and shafts differ between manufacturers and mount generations, so if you are fitting this to anything other than a current EXOS-2 or EXOS-2GT, contact us and we will measure the bore against your shaft before it ships.

Good to Know Before You Order

This is a supplemental counterweight, not a counterweight shaft — the shaft is part of the mount and is not included. Explore Scientific publishes the mass at 9.9 pounds and nothing further, so bore diameter, outer diameter, and thickness do not appear on their page; we can measure a unit in stock if those figures matter to your setup. It is a dense steel object and it behaves like one, so fitting it in the dark above a mounted telescope is a two-hand job with the clutch locked. And if your tube is light and you are chasing a small balance correction rather than a large shortfall, the 5 pound counterweight is the more useful part, since it will sit further out on the shaft where adjustment is finer.

Frequently Asked Questions

Does it come with a locking knob? Yes. Explore Scientific supplies the locking knob with the counterweight, so nothing else is needed to secure it on the shaft.

Can I run two of these on one shaft? Yes, provided the shaft has the free length. Stacking is the normal way to balance the heaviest loads an EXOS-2 will carry, though check the tube itself is still within the mount's rated payload.

Will it fit an EXOS-2GT as well as an EXOS-2? Yes. Explore Scientific lists it for both, and the counterweight shaft is common to the two mounts.

Should I buy this or the 5 pound weight? Buy this one if your current weight already sits at the end of the shaft and the tube still drops. Buy the 5 pound weight if you can reach balance but only at an awkward shaft position, or if you want a finer increment for a light tube.

Bottom Line

When an EXOS-2 is carrying a heavy tube, no amount of sliding will make up for a shortage of mass, and this is the counterweight Explore Scientific supplies for that situation. At a published 9.9 pounds with the locking knob included, it is the direct answer to a mount that will not balance. Tell our team in Bolton what you are putting on the saddle and we will confirm whether one weight will do it or you want two.