Tying tzitzit before conversion

Sometimes my 12-year-old son ties his own tzitzit. He now needs some new tzitzit, but because he’s 12 years and 11 months old, I did the tying myself because if a 12-year-old ties tzitzit for himself, according to most opinions that’s fine, but he may not be able to wear those tzitzit once he’s 13. The case of a non-Jew who converts is similar. Here’s an inquiry on this matter, which we received from Switzerland.

Erev tov. It’s my first time considering to buy a tallit (gadol and katan). I’m doing a Reform gijur and would still like to do the mizvah of wearing tzitzit. My question is: I want to tie my own tzitzit (Rambam-style). If I buy tallits with the option “I don’t need tzitzit”, is there a hole or something to attach my tzitzit? Or would it be better to buy them already pre-tied? (I know, it’s not the same, but I’m not so talented with my hands.) And do I need extra-long ones for Rambam-style? Many thanks for any answer.
Best regards, Nicolas​

Yes, there definitely is a hole, I explained to Nicolas. In fact, you would be in a real bind if there weren’t because it’s actually very hard to make a small round hole with reinforced stitching. The machine used to do it costs tens of thousands of shekels. The smaller tallit makers make an elongated button hole, which is okay, but can be a bit problematic from a halachic perspective.

I told him there’s no need for extra long strings, even if you do 13 chulyot (instead of 7), but recommended you go with thick, because it’s much easier to tie.

I have never understood Reform’s approach to halacha, but just went ahead and wrote to Nicolas what the halacha says: A non-Jew is not allowed to tie tzitzit. If you take a close look at the verses you’ll understand why. That means if you tie the tzitzit before you convert, they would not be considered kosher.

There’s a similar question in a case of a 12-year-old tying tzitzit and then wearing them after his bar mitzvah. But in that case there is definitely room for leniency.