.    .             .  .
 Hilchos Tefillin 32 (page 87) ????? ?? ???? ?? ?? ???? ???? ?? ??? ??? ??????
 The Concept of Mukaf Gevil The Size and Location of a Disqualifying Hole A Hole in the Interior of a Letter
 The concept of mukaf gevil  There is a rule known as mukaf gevil which mandates that every letter of stam must be completely surrounded by parchment. Chazal derived this halacha from the word uchesavtom, which can be divided into two words - u'chesav and tom - i.e. "complete writing." This means that every letter must be formed completely and surrounded by parchment to be fully recognizable. (According to some meforshim, this rule is a halacha l'Moshe miSinai.) There are three areas which require particular attention:  1.There must be space between the end of a line and the edge of the klaf.  2. There must be a distinct separation between all letters (two letters may not touch at any point).  3.  No letter may abut a hole in the klaf. (???? ??, ?"? ??, ????"? ?"? ???; ??????? ??????? ????, 59)
 The size and location of a disqualifying hole In addition to a hole adjacent to a letter, a hole within a letter can also disqualify stam. A hole large enough to be visible invalidates the stam even if it is completely surrounded by ink. If the hole is small, if a quill can pass over it easily [without getting stuck] and if it can be seen only when it is held to the light, it is not significant enough to be disqualifying. A visible hole that formed after the letter was written is not disqualifying, but it should nonetheless be fixed. (One method for fixing it is to remove the ink connecting the hole to the letter; once this distance is created, the hole can be considered separate from the letter.) (???? ?? ??"? ??; ??????? ??????? ????, 60)
 A hole in the interior of the letter Lechatchila?, the rule of mukaf gevil applies to the white interior of letters that close on at least three sides (e.g. beis, heh, ches). Bedieved, according to most poskim, the rule only affects the exterior inked area of the letter and not the white interior. The Yerushalmi, however, holds that the rule extends to the interiors also. When possible, one should be stringent like the Yerushalmi. In extenuating circumstances, the opinion of the poskim can be relied upon. (???? ??, ?"? ??, ?? ????, ????"? ?"? ???)

 All stages of the processing from the lime soak onward must be done lishma. Some poskim hold that if the initial stages were performed lishma, all subsequent stages are considered lishma.   If a goy has access to the hides during tanning (e.g. a goy is working on non-essential parts of the process), he could possibly switch the kosher hides with non-kosher ones. The hides being processed lishma should be marked with a sign that the goy cannot reproduce.   Only the skins of kosher animals may be used for klaf. The skins of kosher animals that died or are otherwise forbidden to eat may be used. The 'size of a small letter' The length of the legs of the letters The size of the left leg of the heh
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