X10SL7-F-O is the retail package with box.
X10SL7-F-B is the bulk package.
-O vs -B model numbers
Many people get confused with these model numbers when they can only find an X10SL7-F-O, instead of an X10SL7-F, or an X10SLM+-F-B instead of an X10SLM+-F. All model numbers are exactly as printed in their respective sections. For real products, they get either an -O or a -B appended to them, for retail or bulk packaging, respectively. An example: A Supermicro X10SL7-F-O is a retail-packaged X10SL7-F motherboard. A Supermicro X10SL7-F-B is a bulk-packaged X10SL7-F motherboard.
What's the difference between them? With retail packaging, you get a box, with proper packaging materials. With bulk packaging, you get something along the lines of an antistatic bag, a bit of protective foam and some cardboard to wrap it all up.