What I did is call
Scamp, have them year of my trailer and that it was a 13 standard. While Devon rattled off sizes and applications, I wrote it all down on a print out from my computer/printer of their rivets page. Since some of the rivets are for the 16, I knew they didn't apply to me.
However, I must share that on two occasions the recommended rivet length was too long, hence a sloppy fit. Calling
Scamp about it, they mentioned that in places, the FG shell can have varying thicknesses. Just something to be aware of when you choose the correct Scamp rivet and it doesn't work length wise!