How do you ship coins as lettermail? (this question is not about me)

[vintagetonow2134]

I found some coins (won't say where or how) They are somewhere on ebay. 

I want to bid on them. That guy says he will ship them as lettermail. But how does that work for coins isn't the envelop likely to rip apart? 

[vintagetonow2134]

American DImes and shipping is free within Canada Regardless.
Neither of the ones you said.