Size of DVD writer in Vostro 3458

Hello, what's the size of Dell Vostro 3458's DVD drive? Is it 9.5mm or 12.7mm? I'm planning to add an SSD, and use the HDD with the help of a caddy. That's why I need to know which size of caddy should I buy. I tried finding the answer in device manual and also on website specifications but couldn't find it. Thank you