The M6 cabinet knock-down fitting system is well-known and widely used as it is a simple, yet effective way of assembling furniture that may require dis-assembly in the future and is attractive so if it must be visible, will not detract from the appearance of the furniture.
The bolts have a standard M6 thread and are produced from steel with a nickel-plated brass finish. The length is the shaft length - all the heads measure 17mm diameter and are 2mm thick. They use an M4 allen key head to tighten.
Also available is a corresponding cap nut so that if a through-hole needs to be used, it looks identical from both sides. The cap nut requires a 9+mm hole for clearance and increases the working length of the bolt by 10mm. In other words a cap nut used with a 25mm bolt can bolt together a maximum of 35mm.