Yesterday I borrowed a digital micrometer - which can be used to measure the thickness of paper.
Thought I would take measurements on my collection of Hero Quest rulebooks and contribute my findings here.
You will see numbers for my
North American (US) books
British (UK) books
Danish (DK) books
I also measured thickness of the cards I have, as well as a couple of sheets of "normal" printing paper I had - for comparison.
All measurements are in millimetres (mm). You should be able to convert into your local units wherever you are in the world.

Sheet size is the size of the paper sheets before they are folded and stapled.
I don't have the equipment to measure how glossy the surface of the paper is, so I'll just give my impression.
Hero Quest - Rules of Play (UK - 1989 version)
Sheet size: 286 mm x 205 mm
Cover thickness: 0.07 - 0.08 mm
Page thickness: 0.07 - 0.08 mm
Cover glossy, pages glossy
Hero Quest - Rules of Play (UK - 1990 version)
Sheet size: 299 mm x 211 mm
Cover thickness: 0.08 - 0.09 mm
Page thickness: 0.08 - 0.09 mm
Cover glossy, pages glossy
Hero Quest - Rules of Play (DK - 1990 version)
Sheet size: 299 mm x 213 mm
Cover thickness: 0.08 - 0.09 mm
Page thickness: 0.08 - 0.09 mm
Cover glossy, pages glossy
Hero Quest - Quest Book (UK - with "The Trial")
Sheet size: 298 mm x 210 mm
Cover thickness: 0.22 - 0.23 mm
Page thickness: 0.07 - 0.08 mm
Cover glossy, pages glossy
Hero Quest - Quest Book (DK - with "The Trial")
Sheet size: 296 mm x 210 mm
Cover thickness: 0.19 - 0.21 mm
Page thickness: 0.06 - 0.07 mm
Cover glossy, pages glossy
Kellar's Keep - Quest Book (DK)
Sheet size: 296 mm x 212 mm
Cover thickness: 0.21 - 0.22 mm
Page thickness: 0.07 - 0.08 mm
Cover glossy, pages glossy
Kellar's Keep - Quest Book (US)
Sheet size: 229 mm x 302 mm
Cover thickness: 0.26 - 0.27 mm
Page thickness: 0.12 mm
Cover glossy, pages matt
Return of the Witch Lord (UK)
Sheet size: 297 mm x 209 mm
Cover thickness: 0.20 - 0.21 mm
Page thickness: 0.07 - 0.08 mm
Cover glossy, pages glossy
The Frozen Horror - Quest Book (US)
Sheet size: 226 mm x 305 mm
Cover thickness: 0.11 - 0.12 mm
Page thickness: 0.11 - 0.12 mm
Cover matt, pages matt
UK Hero Quest cards thickness: 0.27 - 0.30 mm
US Frozen Horror cards thickness: 0.25 - 0.26 mm
And for comparison:
a sheet of 80 grams paper: 0.10 mm
a sheet of 100 grams paper: 0.11 - 0.12 mm
I was surprised at the small variations in sheet size, so I asked someone who had been in the printing business. He told me that normally printing is done on sheets that are a bit too big for the final product, and then at the end they are cut to the size wanted. Small variations then occur in the exact size of the cut. Also, the sheets are cut after they have been folded and stapled, which makes the innermost pages a tiny bit smaller than the outer ones.
Enjoy!
