I have been building boat shuttles for the past few years to hold 4" to 6" bobbins. I've had some requests recently to make quill shuttles. I'm wondering what are the most useful sizes for quill shuttles for overall length and cavity length? I'm assuming that the cavity length should be an inch longer than the length of the quill for adequate movement back and forth. Is there an ideal height for the shuttle (somewhere between 5/8" and 1"), and are open or closed bottom shuttles preferred? Thanks for any advice!