Justrite - I got this old Justrite shuttle from a Yahoo Auction. It says "Justrite" and "Pat. Applied For" on it.
It twists apart into two separate leaves so that the thread can be easily wound on.
This is an old shuttle, perhaps from the'20s - I'm not sure. it is not made anymore, although there are replicas, which can be obtained from some of the shuttle suppliers out there, such as
Lacis
Here it is twisted open and separated, so you can see the inner parts.