ב"ה, כ"ג תמוז, תשי"ג
ברוקלין.
שלום וברכה!
... בטח ידוע לו שבנוגע לנשים הרי ע"פ מרז"ל (בכורות מה, א) שנר"ב אברים להן, ולכן נוהגים לכתוב, לכל אברי' ושס"ה גידי', ואמאן דלא קפיד - לא קפדינן. והכל שלום.
B"H, 23 Tammuz, 5713.
Brooklyn.
Shalom u'Vrachah!
... It is surely known to you that regarding women, according to our sages of blessed memory (Bechoros 45a), they have a different number of limbs. Therefore, the custom is to write: 'to all her limbs and 365 sinews.' And if one is not particular about this, we are also not particular. All is well.
Summary
The Rebbe explains that for women, based on Chazal's teaching about their number of limbs and sinews, there is a custom in blessings or prayers to specify this difference. However, strict adherence is not required if one does not wish to be particular.