I don't see my tablet listed in the compatibility section for this cradle. How can I make sure my tablet is compatible before placing an order?

You can find a list of compatible dimensions for this holder in the product information section. If you want to make sure your tablet will fit in this holder you can measure your tablet to make sure it falls within the compatible dimensions.

Will this holder not work if the additional side supports do not fit my tablet?

In most cases this should not be an issue. The additional side supports are optional to keep your tablet secure in extreme, high vibration environments; or if you are supporting the tablet in portrait mode, it is recommended to install one of the supports to hold the bottom of the tablet.

How is it that this holder fits 9" - 10" tablets, yet it can also hold the iPad Pro 11"?

The 11 in iPad Pro 11 refers to the diagonal dimension of the screen display. Overall dimensions of this tablet are 9.74" x 7.02" x .23", which fits the dimension ranges of this holder. For all universal holders including the RAM® X-Grip®, it is a matter of cross referencing overall dimensions (L x W x D) when determining compatibility. Case dimensions will need to be taken into account if your tablet is in a case.

Im going to need the optional arms for the x grip universal holder on my sailboat. Are they included or do you buy them separately?

This is just the tablet holder so you will have to buy the rest of mount separately. If you go through our  BUILD-A-MOUNT you can seeif we offer this in a kit. You can also hit the COMPLETE YOUR SOLUTION tab andsee the compatible components for this tablet holder. 

I have a Microsoft surface pro with dimensions of 11.5" wide x 8" h and a diagonal of 13.75" . Will the RAM® X-Grip® Universal Holder for 9"-11" Tablets fir this tablet?

The RAM-HOL-UN11U is a better fit for those dimensions and for all of the MS Surface Pro tablets. 

I have a Vector bar in my JKR. How would I mount the X-Grip for my iPad Air?

You can hit COMPLETE YOUR SOLUTION on this product page. Then hit SEE ALL; from there you can filter to the left of the page and filter your clamp range to accommodate your bar size.

does this mount work with the B class mounts or does it have to be paired with the C class

You can use either the B or C size components to mount a RAM-HOL-UN9U.  RAM recommends using the B size components if that cradle will be mounted in a static environment and use the C size parts if you'll be overlanding, off-roading, or in a high-vibration environment.

This part says it has a maximum height of 10.25" (using optional supports). Is it possible to use this cradle with a tablet that is taller than that?

Yes, the maximum height listed only applies if you are using the optional side support arms. If you leave at least one of those arms off of the mount it will be able to support taller tablets.

I have been using this mount with a large tether that I bought from you. I cannot find where to order more of the large tethers that will secure 10 inch screens to this X-grip holder.

The largest tether we make for the X-Grip style tablet holders is the RAM-HOL-UN8TU.