words - Define the terms used for "types" or "grades" of tefillin

Follow up on this M.Y. question:

The questioner mentioned these grades of tefillin:

• Peshutim


• Mehudarim



• Dakos


• Gassos


• Gassos Prudos

I have heard of some of these terms, but there may be others on this list that I am unaware of, so please edit.

I am uncertain what these terms mean. More curious, why are each of these important, practically? If you can include some history / background to when the grade issue occurred and / or some sources, I appreciate that.

Answer

Tefillin are divided into different categories based on the quality of the leather boxes

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  Tfilin crafted from two separate pieces of leather (which are then glued together) are known as tfilin peshutim, the simplest tfilin. Hasofer says they generally last only three to five years, after which the pieces begin to separate and they lose their required square shape making them invalid for use

  
  


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  Tfilin made from one very thin piece of leather are called tfilin dakkot, thin tfilin. They are made from a single piece of high grade but thinner leather. The required perfectly square tefillin shape is produced by folding and gluing the leather, or in some cases by stretching the leather over a frame and folding it into shape

  
  


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  Tfilin formed from one very thick piece of leather are called tfilin gassot, thick tfilin. These are the most durable (and expensive) kind. It is more difficult to make and only became available in the last century or so. The leather is stretched over metal plates and folded and pressed at very high-pressure to form the familiar perfectly square tefillin shape. They will last up to 50 years when properly maintained but are of course more expensive

  
  


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  Mehudar (as in pshutim mehudarim or dakot mehudarim) refer to more hiddurim (enhancements)

  
  
  


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  Prudot (separated) refer to the way the four compartments of the shel rosh are separated. Most tefilin gassot are rov prudot, which means they are separate most of the way down, but some glue is applied toward the bottom to help the tefilin keep their shape over time. Tefillin Prudot are completely separated, to meet the stricter opinions. However, note that in some cases they do not retain their shape and have to be reshaped after a few years. Standard tefillin gassot and prudot look almost identical on the outside

  
  


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  Mikshah echad (one piece): see here for a related answer

  
  

The reason the quality levels are important is simply than the higher-quality will maintain their shape (and kashrut level) much longer. Unless one is on a strict budget, there is no reason today not to buy tfilin gassot. Even economically, it is much cheaper to buy high quality tfilin and keep them 50 years than cheaper ones that need regular fixing/replacement.

The "technology" used to manufacture gassot has only been developed at scale in the last century which is why the tfilin we wear today are of incomparably better quality than those worn by the greatest sages of previous centuries. A wise rav once told me this was because, as we were descending spiritually, maybe we need better religious objects to compensate...

See here, here and here for more sources which I partly leveraged to assemble the definitions above

And here is the best book I found on the intricacies of making tfilin and stam in general. Fascinating reading.