How do Chaba"d shluchim size tefillin shel Rosh for everyone?

Question

I see many Chaba"d shluchim have Jews put in tefillin. Wonderful work their doing. However, I read this in Aruch Hashulchan O.C. 27:20:

ומקום הנחת תפילין של ראש מהתחלת עיקרי השיער שעל המצח עד סוף המקום שמוחו של תינוק רופס ויש להזהיר לההמון על ככה, כאשר ראינו בעינינו שרבים נושאים השל ראש חציו על המצח. ואוי לאותו בושה, כי לא קיימו מצות תפילין מימיהם, ומברכים לבטלה, ועונשם גדול

Summarizing the above:

The proper place for the tefillin shel Rosh is from the top of the hairline until the point of where a baby's forehead is soft. One should be especially careful about placing the tefillin in the proper place, for if not, this is a terrible embarrassment to the mitzvah, they have made a blessing in vain and the punishment is great.

My question - the tefillin shel rosh strap is one size. Are the Chaba"d shlichim adjusting the strap for each person's head before they have that person say the bracha? If they aren't, how can they let that person say the bracha?

Answer 1

As pointed out by @Noach in the chat, the Chabad minhag is to say only one beracha on tefilin. That is they say the beracha of lihaniach tefilin before tightening the tefilin shel yad, and no beracha on the tefilin shel rosh, unless one spoke or otherwise interrupted between the one tefila and the other. (This is also the Sefardic minhag. The Ashkenazi minhag is to always say the beracha of al mitzvas tefilin before putting on the shel rosh.)

A second point that must be kept in mind is that the two tefilin are two separate mitzvos, and one can fulfill one without the other. (O.C. siman 26)

Because of this, the Chabadnick does not need to be overly concerned about the tefilin shel roash. Of course he will try to make sure that it is tight and in the proper place, and probably would adjust the knot if it were obviously too big. But even if the shel rosh is not put on correctly, since no beracha is made, the one putting on tefilin is only better off that if the Chabadnick hadn't come along, having certainly fulfilled the mitzva of TSY and maybe also TSR without a safek beracha.

Answer 2

I believe they typically have multiple Tefillin bags at their booths for different head sizes and they are quite good at adjusting the knot on the shel rosh if needed. I believe they put Tefillin on people based on the Shulchan Aruch Harav and am not aware of any heter kiruv on this point that they hold by.

Answer 3

There is some amount of space between the hairline as the forward most boundary and the fontanelle as the back boundary. It is presumably possible to size tefillin such that they will be in this range on most people, closer to the hairline on small heads, closer to the fontanelle on large ones. On my own head, it feels as if I can just barely fit 4 fingers in this range. Granted, because the tefillin must be entirely within these boundaries, one must deduct the size of the tefillin themselves from the range of acceptability (if there is say 3 inches of space, and tefillin are 2 inches, there is an inch between the furthest back tefillin may be and the furthest forward.)

There is a chart here of head circumferences in adults, which seems to be, somewhat unsurprisingly, a factor of height. Assuming one wants to get say the middle 50% of head sizes in men of all heights considered in that study, one finds only a range of 56 to 60 cm.

So there isn't huge variation in head size, and there is a range of acceptable sizes for any given man, so an average sized tefillin should fit most men.

The people who stand in public places encouraging men to put on tefillin are also well practiced at adjusting them.

Answer 4

Sure, people have different sized heads, but the difference in size is never drastic. People more or less have similarly sized heads. That being said, it is not difficult to adjust the knot on the Shel Rosh at all.