Locking-cap module and connector

A locking-cap module may include a locking-cap having a first connecting flange and a second connecting flange opposite the first connecting flange extending from a side surface of the locking-cap. The locking-cap may further include a first retaining rail and a second retaining rail opposite the first retaining rail. The locking-cap module may further include a set screw configured to engage with corresponding threads of the locking-cap. In some embodiments, the first connecting flange and second connecting flange are configured to engage with a connector such that the top surface of the locking-cap is flush with a top surface of the connector in an engaged position. In some embodiments, the set screw is initially coupled to the locking-cap by a pre-loaded connection. In some embodiments, a surgical tool is provided for rotating the locking-cap module into the engaged position.