That's part of what you need if you want to use the supplied L&M ball mount. Assuming that it's also a 1" ball (likely is) you'll also need at least a 1" clamp to connect the two balls together - this one:
Ikelite | Clamp for 1 in Ball Arms Arms
Most people would add a second clamp with an arm between them to get the light further away from the plane of the camera for less backscatter.
So two of these:
Ikelite | Clamp for 1 in Ball Arms Arms and one of these:
Ikelite | 1 in Ball Arm 9 in Length
That stuff gets pretty expensive fast. Two clamps and that arm and you're looking at $125.
A much cheaper option is to use the other Gobe supplied "flex" adapter. I'm guessing it's 3/4" based on it's relative size compared to the ball.
So then you buy one of these - snap off the Ikelite specific top and snap your Gobe mount on.
Ikelite | Flex Arm for DS51 It's $60.
Or buy the snap-in handle and 3 sets of flex segments separately for $50. One of these:
Ikelite | Flex Mount for Quick Release Handle and 3 of these:
Ikelite | 3/4 in Flex Extension (4 piece)
An even cheaper option is to buy only the Ikelite snap-in mount and buy the flex arm (also called Loc-Line) segments on eBay. Just make sure they're 3/4" and loc-line brand - there's some other non-interchangeable systems sold there. Often the real loc-line comes in Blue and Orange also.
Reef Photo also sells the 3/4" arm segments for $1 apiece.
Loc-Line : Reef Photo & Video!, The Underwater Photo Pros
Should you want to later move the light to the non-handle side of your tray you need a base mount adapter - like this:
Ikelite | Flex Mount for Steady Tray Those are also $8 instead of $20 if you can drill a hole in one of these and find a non-corroding bolt/nut.
Loc-Line 3/4\ Fixed Mount aka Base [loc.60533] - $8.00 : Reef Photo & Video!, The Underwater Photo Pros
FULL DISCLAIMER: I haven't ever physically handled either your tray or your light. But I'm pretty sure I'm right...
My buddy uses a clamp/ball system for his video light and I have prior experience with the loc-line segments.
You might also check locally with a hydraulic/machinery supplier. Loc-Line is actually used as cooling hose for industrial equipment. Here's the original mfr's website - others make it now also:
The Original Modular Hose System | Loc-Line We have WW Grainger here in the states, a complete kit like the last one I described is all of about $15 for the base mount and the arm segments.
