The "clamp" is integral and the plate comes with it.
Mine arrived this week, and I must say I'm very impressed with it. It's noticably better than the Benbo ball and socket head I have been using, despite costing less than what I paid
second hand for the Benbo head.
Great piece if kit
Thanks for that Mark, that's just what I wanted to hear - I think I must go and click on a few buttons and get myself one of these

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Originally, I wanted to upgrade the clamp on my Giottos ball head to a (27 quid) Arca style clamp, but it seems that they don't fit properly without drilling a counter-sunk hole into the plate first, and I don't have the tools to do that :shrug:.
So, I might as well spend another 23 quid and have an RSH-12 for my tripod and just and use the Giottos on my monopod

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If only all camera equipment was so reasonably priced

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It comes with one plate, but it's not spectacular...
I highly recommend getting some better plates, although you need not spend £50 per plate as some are (eg Kirk). There are chinese copies of the wimberley plates on ebay, which have identical anti-twist nubs and safety stop screws, but come in at less than half the price. I have genuine wimberleys (bought before the chinese ones were available) and a colleague bought one of the chinese ones and they are absolutely identical (even down to the connections for the wimberley flash bracket, which kirk and markins plates do not have) - I'd have no concerns over buying the chinese ones. They're £15-£20 each.
Don't bother with plates that have little rubber bits or cork on. Properly designed all-metal plates are better as they provide one less place that movement may be introduced.
Thanks for the info about the plate I-S

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Ultimately, I want to get an L bracket (Kirk, probably) for my D700 and the little square one supplied with RSH-12 would simply be to hold my (plastic) D90 with a short lens on. I just wondered whether or not I needed to order one of these as a separate item, or whether one was included.
If it
wasn't already included, I'd take your advice and so and look for a better one, but as it is included, I can try it out first and get a better one if it's no good.
Thank you both for your help

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