^ Thanks! That was helpful. I was afraid that if the 20mm had a kind of loose fit, the 19mm might be even worse (although it is only about 1/25th of an inch difference). Especially with something slightly compressible in the ends, it should keep things from moving around too much.
With that in mind, I went ahead and placed an order only to receive this response:
Quote from: McMaster-Carr
Thank you for considering McMaster-Carr for your purchase. However, we will not accept orders from your facility due to the cost of complying with US export regulations.
Sigh. I must admit I am pretty surprised, as I order stuff from the States all the time. As long as I am willing to absorb the added costs, it has never been a problem. Oh, well. I will be over there in mid-July, so maybe I will try to get some delivered to my hotel...