Kris presented the following explanation :
Anyone know if the glue used in magazines to fix extras like
cover disks etc. can be purchased ?

It is a like a clear rubbery mastic which fixes well but can be
peeled away easily without leaving marks or ripping the paper.

Ta, Chris

Despite the replies given by others, it looks very like hot melt glue
to me. The type you get in sticks to feed into one of those cheap guns.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.org