Q. Re- questions (2559-60) above. How much is one obliged to be concerned about the possibility of having shatnez in one’s clothing, to be machmir and pay for a bedika or shaatnez test?
A. Ramban (Chulin 12a) and others compare this testing to the examination of the lungs after shechita, done in cattle or for the presence of insects in some fruits and vegetables.
Mishkenos Yaakov (Y.D. 17), asserts that you only have to be concerned for a regular possibility of ten percent, and that is called “miut hamatzui.” Others are far more lenient and maintain that a frequent possibility could be even close to fifty percent and we should not be concerned for less than that. (Ribosh 191). On the opposite extreme, some assert, quoting Igrois Moshe (Y:D 1:72) that even garments that one is not obliged to test for shatnez, but there is a slight doubt, one should preferably have them checked. They mention that it is even only a one percent possibility, See also Shevet Halevy 4: 81
As mentioned before, Horav Shlomo Miller’s Shlit’a opinion is that one should consult with a tester or a Rov familiar with the specific manufacturer, and the type of clothing involved before making an educated and common sense decision on a real situation.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit’a