Different size computers
The size of a desktop computer varies and generally come in two categories: towers and small form factors (SFF).
Tower computers have more empty space inside them to accommodate future upgrades, whereas SFF computers are designed to be compact and so have less free space inside.
In order to fit a USB 3.0 PCI card into your computer you need to make you you get the right size bracket.
The sizes are 12cm and 8cm.
For tower computers you will need a full or standard size bracket (also known as full or standard profile).
For small form factor computers you will need a low or half-height size bracket (also known as low or half-height profile).
Full desktop tower or mid tower computers
If you have a full desktop tower or mid tower computer a standard profile bracket card will fit.
If you have a small form factor pc you will need to check that the card includes a low profile bracket to fit your smaller computer case.
Both these cards include full and low profile brackets and so can fit in both SFF and full desktop computers:
The 2 sized brackets are interchangeable and are fitted in the same way.