Try starting with a f3 (.003) for coursish stomach hair. You’re learning to do insertions so I dont think the solution is to start with too large a probe, you can increase probe size once you have the insertions down pat. The idea in general is to at least match the diameter of the hair being treated. You can be forgiven using a slightly smaller one, while you learn to insert first.
I get to work on all different kinds of hair, and it does call for all sizes of probe. I like to use alot of f3’s and sometimes f2’s on upper lips. I have 2 clients I use f1’s for their fine little vellus hairs ( only dectro protec makes these) . For trans faces I go to a lot of f4’s. I dont often get call for f5’s or f6’s but they are there if I need them . Most commonly used i think are f2, f3, f4 but that’s just me
When I did a lot of blend, I used a lot of gold, then realized I was having just as easy insertions with plain stainless ballet, or sterex one piece needles. I do mostly pico and synchro thermolysis now. We are using mostly protec probes around the office now, in either isoguard or isoblend, each have their strengths.