The mechanical on/off detent of the dimmer on a 120 volt, 100 watt halogen lamp failed (i.e.: lamp always on but would still dim/brighten). The failed pot was labeled SB250K and part of a diac & triac circuit I could figure out.
Using a digital meter, I confirmed my suspicion that the pot's resistance was ~250kΩ and was linear. When searching for a replacement, I found identical mechanical layout (e.g.: diameter, shaft length, contacts positions, etc.) Electrically, those replacements were also 250kΩ with linear taper and had five identical contacts: 3 traditional pot contacts (top of photo) and 2 on/off switch contacts (rear). But in all cases, were labeled B250K (and not SB250K). I took a chance, ordered one of these and it has worked fine.
Is it important that I could not find a pot labeled SB250K? What does the letter S signify?