The jigs used for worktop joins can handle both 28mm and 40mm worktops, as already suggested. The element to check is whether your straight bit is long enough to complete the through cut. Only take off a few mm at a time and never more than 10mm at one pass. The cuts are made in order that the joint is both tight and attractive, but this requires a little practice, so a few pointers may help:
1) When using the router, you MUST follow the jig instructions regarding cutting direction, otherwise you will get tearout of the laminate finish where the cutter exits the workpiece.
2) The use of butterfly bolt fixings on their own is usually sufficient, although I prefer to add two rows of biscuits to assist horizontal lining up (to make sure both surfaces are coplanar).
3) Whilst it is perfectly possible to calculate the position of the joint along the workpiece, I prefer to cut the join first, then offer up to discover the actual length before cutting off the excess.
4) Prior to cutting the joints, both male and female, I also run a trimming cut across the ends to remove the dinged shoulders so often found due to knocks in transit.
5) Make ABSOLUTELY sure that you've got the workpiece positioned with the correct surface facing up when positioning the jig. Make sure that your clamps will not impede the path of the router.
6) When considering which way round to cut the joint (i.e. which piece will have the male or female joint), bear in mind where this will come in relation to the base unit sides. This can affect the ease of access to the butterfly bolts. Consider also where the sink cutout will come, particularly if it's a full cut-out for the draining board.
7) When tightening the bolts, make certain that both parts are absolutely flat.
Any other questions, drop me a PM.
Ray.