what size is the opening to hold a cup? what diameter cup can it hold?

The lower cup has no role in holding any cup. As for the upper cup, a 30oz YETI Rambler doesn't seat to the bottom of the cup. Only about 2/3 of the YETI tapered bottom, fits into the cup, so the Robo-Cup is holding it via friction fit, NOT because the cup ever properly seated on the bottom.

will it hold a red solo cup?

Yes it does and in addition we now also have available the RoboCup Plus as an add-on accessory which holds large sized drinks. Thank you. -- RoboCup Family

does it clamp onto a beach umbrella

Yes it will. It is very powerful and can be difficult to open widely to attach to larger diameter objects. it works on my beach umbrella, my favorite chair, and rolling tackle box. My umbrella is no larger than one inch diameter. It could be difficult for larger diameters, but I love it. Very durable.

Colour	Red,Black
Material	Resin
Brand	ROBOCUP
Manufacturer	RoboCup
Automotive Fit Type	Universal Fit
UPC	856341001158
Batteries Included	No
Material Type	Resin
Size	Standard
Style	Standard Spring
Country of Origin	USA

ROBOCUP 12 Colors, Best Cup Holder for Drinks, Fishing Rod/Pole, Boat, Beach Chair, Golf Cart, Wheelchair, Walker, Drum Sticks, Microphone Stand

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