can someone please help with hole dimensions

[routercnc]

Ash,

Keeping it simple - to bolt part A to part B with a flush fitting M8 cap head:

1. If you are doing the work:
Part A- scribe centre of hole, use centre punch, spot drill and then drill a through hole with diameter 8.5mm drill
Part A- use an M8 counterbore tool (has diameter 15mm) to a depth of 8mm (same as M8 cap head depth)

Part B- mark out, centre punch, spot drill, and then drill a pilot hole of 6.8mm diameter
Part B- use an M8 x 1.25mm tap to create the thread (keep it straight in the hole)

Tidy any raised burrs left on either side of part A or B using a countersink tool - otherwise they will not sit tight against each other
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2. If you are making a drawing for someone else to make:
Part A- label hole circle as "dia 8.5", label counterbore circle as "CB dia 15x8"
Part B- label hole circle as "M8 x 1.25" (they will know to drill it 6.8mm, tap it, and do the countersink tidy up)

If you have multiple holes which are clearly all the same you can use " (xx places)" after the dimension. For example if you have 5 holes all the same you can label just one with the text "dia 8.5 (5 places)".
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Notes:
Be aware that an M8 bolt is actually slightly less than 8mm in diameter so the hole could be 8mm but the 8.5mm clearance will give you some adjustment. I use 8.5mm (rather than 8.4mm) because 0.5mm steps come in the regular drill sets, although you can buy drills in various sizes such as 0.1mm steps.

If for some reason when you put it all together that you need a bit more adjustment to account for slight errors in other parts, it is no big deal to drill the 8.5mm hole out to 9.0mm, so don't sweat the 8.1 vs 8.4 vs 8.5 dilemma. Important thing is to get a hole in the right place.

If you have a more complex part with counterbores on the upper and lower surfaces (or any detail on other faces) then you need to draw all relevant views. To understand this read up about 3rd angle projection which is a standard for laying out the top, side, bottom, front, back, of any part in an unambiguous way that the machinist will understand.
If you try to label a counterbore on the underside of the part by pointing to it on the upper surface drawing you will cause confusion and might get the CB on the top instead.