The cap back fixture is a special fixture that was designed for customers that embroider a lot of cap backs. Most customers do not need this special fixture.
Go to this link for an explanation of the differences between the fixtures.
Cap Back Description PDF

The 12cm size is the most common size that customers order the cap back fixture for. We have 12cm and 15cm available for most brands, we will contact you if your brand is not available after receiving your order.

Size of Fixture

12cm 15cm

Brand of Hoop or Machine the fixture is for