EDIT 8/5/2020: the AK51H rivets identified below won’t work. See my later post regarding countersunk rivets.
In my part 2 post regarding the fuselage side skin install, I noted that the TSi instructs you to use 4.0mm rivets to attach the skin in the dimpled locations, rather than 3.2mm rivets. I sent a message to Sling Aircraft tech support, and once again got a reply directly from Mr. Mike Blyth, one of the founders of Sling Aircraft.
As it turns out, there is a good reason to upsize to 4mm. Because the holes were drilled at the factory with the intention of installing 3.2mm domed rivets, they are drilled to 3.3mm. The process of dimpling causes the hole to grow in size – up to 3.8mm, according to Mike. Indeed, when I took my calipers out to measure the holes, I measured ~3.7mm, which is larger than the max allowed 3.38mm size for the AK41H rivets I ordered. 3.7mm is too large for any 3.2mm rivet, by the way, so the only acceptable solution in this case is to go up to the next larger size, which is 4.0mm or 5/32″ in US.
Luckily, I found another place to source the rivets – POP AK51H in this case – from BlindRivetSupply.com. I ordered the rivets on Monday and to my surprise they’ll be here Wednesday, coming from a warehouse on Long Island, NY.
Unfortunately, this means I have to drill out all the rivets I already installed. I will also need to re-dimple the holes with a 5/32″ dimple die, so for that I turned to Aircraft Tool Supply, where I ordered that and a few other things on my shopping list.