Can I bring beehive frame spacers with me to the USA as hold luggage?
And on the flights to the USA, are these not allowed as carry on baggage?
The TSA webpage covers things you can bring in your checked and carry on baggage. It is not clear what aspect of the item makes you think it is not allowed. Assuming the object meets the size requirements and is just made out of aluminum there should not be a problem. For example, saws are allowed in checked baggage, although they should be sheathed or securely wrapped to prevent injury to baggage handlers and inspectors.