Standard Batim are on average 33/34/35mm. For those who do a lot of traveling where every ounce is counted, and every inch in the suitcase is important you may want to consider these 28mm batim.
Weighing approx 8oz, which is half the weight of standard Tefilin and nearly half the footprint these are the smallest Gasos batim that can still hold a "regular size" Klaf for the Parshios, anything smaller will effect price and quality of Parshios considerably. As the Parshios will have to be written on smaller Klaf and the Ksav needs to be written smaller,
Most Sofrim are not ready to write so small and many are not able to do so, as it is very difficult to write Parshios properly with all the details in such a small size. The Sofer must write slower then he is accustomed to, it is much more strenuous and he must be of a much higher caliber to be able to write beautifully so small.
Parshios in this size are approximately $400+ more then equal quality Parshios in the Standard size Klaf.
As well there are many more options of Mehudar Parshios in the regular size Klaf.
Rabbi Kass was ordained by Rabbi Yisrael Meir Lau, former Ashkenazik Chief Rabbi of Israel. He is certified as a Sofer for both Kesivah and Hagoah by one of the leading experts in Safrus, Rabbi Avrohom Tzvi Vosner, Rav of the Vad Mishmeres Sta”m.