This is a ski boat fitting. It is used to hold the wakeboard rack on the boat tower. The URL supplied shows how it is mounted. These are made by numerous manufacturers in many different inside diameters for the size of the tower tubing. Some use a rubber insulator and some don't. The maker of yours is unknown but it is almost identical to the one shown in the second URL supplied.

It is a likely mount for motor cycle handle bars. Judging by the robust nature it is adaptable for various instruments (tack, speedo, Etc) or possibly even a light. In the world of custom motorcycles the possibilities are endless. I could not get an accurate size on the internal hole from the pictures so it could also be a clamp for the front fork maybe a light or fender. here is a link showing a similar clamp but lighter weight. Either way it is motorcycle related and your local Harley Davidson shop could shed better light on its intended use. Good luck.

References:

http://www.marlinsclocks.net/Marlins-Quest-Compass-in-Classic-Adjustable-Hand...

Reason:
Thank you for your opinion. Perhaps if you could find a clamp that mounts to a flat surface in the same way as this one, I could accept the opinion. I can't seem to find any that have a flat surface mounting area like this one.

This is a ski boat fitting. It is used to hold the wakeboard rack on the boat tower. The URL supplied shows how it is mounted. These are made by numerous manufacturers in many different inside diameters for the size of the tower tubing. Some use a rubber insulator and some don't. The maker of yours is unknown but it is almost identical to the one shown in the second URL supplied.

References:

https://www.ebay.com.au/itm/Bat-Holder-Wakeboard-Tower-Rack-1-5-8-1-3-4-1-7-8...