What is the recommended gap for clay pavers?
The gaps on the pavers are 2mm to 6mm, which are to account for both PA and PB pavers so that lines may be maintained. (see the tolerances in the spec’s on both types of pavers)
The "nibs" technically are only to assist with laying and are not for any structural reason. Most nibs are offset so as not to end up contacting each other, but strictly speaking, the jointing material is designed to diffuse the lateral and vertical forces by transferring them through to the bedding sand and sub-bases layers.
It is highly recommended that the grade of jointing material is different to the bedding sand, to expand in the joints and create the lockup. It must also be vibrated so that it fills the joint to the bottom and in so doing allow the forces to be transferred through. Again, one of the more important issues in the design is the edge restraint which holds the whole system together, and patterns relevant to the usage are also critical.
Please download the "Movement of Brickwork" technical paper.