This is sometimes known as mounting putty, poster putty, white tack, or similar. It is great for sticking Metal Marshmallow contact mics to almost any surface. It is transparent to sound. This putty holds very well by itself, but for maximum strenth it can be used in conjunction with
double sided tape
Note that there is a LOT of putty here and it is reusable, so one package might be more than you will ever need.
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