When buying tefillin and mezuzot, and even a Sefer Torah, it is important to understand the proper shapes of the letters. Every letter has a proper structure. However, while there is general agreement regarding the tzura (shape) of the letters, they are many different customs regarding different aspects of the letters. For example, there are three common customs: Beit Yosef, Kaf HaHaim (in his Kol Yaakov), and Minhag Sofrim (often called Ktav Vellish, which is the most standard writing for Sephardim). There are numerous differences between these three customs.
For example, the letter "heh" is constructed from a resh, and a vav. It is customary to put a "tag", a crown, on the letter heh, a little to the right of the upper left corner, as it is customary to draw single tagim on the letters bet, dalet, hey, het, yud, and koof, often known by the acronym "bedek hayah. The leg of the heh is generally shaped like a diamond- narrow towards the top, and thicker in the middle.
It is interesting to note that the Ari z"l has a unique hiddush regarding the shem Hashem (yud, heh, vav and heh), the name of God, as it appears in the Sifrei Torah. According to the Ari z"l, the first heh differs from the second heh. On the bottom of the leg of the first heh, i.e., on the right side, there is a "pesia lebar" literally a step sticking outwards. The second heh is a regular diamond-like shape. A person who is buying a Sefer Torah should be careful to purchase one in which the first heh of the shem Hashem is written in this manner. A Sefer Torah without the pesia lebar is not mehudar.
Needless to say, if the left leg touches the roof, the letter is invalid (pasul), as it looks like a het. However, as long as there is a slight separation between the left leg and the roof, it is valid, but not mehudar. Finally, preferably the two legs of the heh should end at the same point. If the right leg is longer, it may look like a koof.
Summary: every letter has its own characteristics, and it is important to be familiar with the characteristics of each letter when purchases a Sefer Torah, tefillin or mezuzot. We noted that the letter heh is constructed from a resh and a small vav, the vav is usually somewhat diamond-shaped. There should be a kotz on the top of the left leg of the letter. When the vav is part of the first heh in the shem HaShem, the minhag HaAri z"l is to draw a "pesia lebar"- a small line saving left.
