What is the true pinyin pronunciation for this radical?
The glyph「丨」is called gǔn as a dictionary radical, and appears in most dictionaries including the Kangxi Dictionary, Xinhua Zidian, and Xiandai Hanyu Cidian. It is a homograph of the character stroke shù, which just means vertical (line), but this name is not the proper one used when referring to the radical.

The pronunciation of「丨」can be verified in e.g. the Kangxi Dictionary:




  「丨」, Jiyun: Fanqie initial gǔ and rime běn.


Characters which are grouped under「丨」commonly are done so because they couldn't be easily grouped under something else. The vast majority of these characters have a vertical stroke as a prominent feature in the character, and this is about all that they share.

The following are the only commonly used characters which are grouped under「丨」:

个, 丫, 中, 丰, 串, 临



As @dan mentioned, many people wouldn't understand what exactly this radical is (myself included, before I looked this up), because in general, radicals are not an intrinsic feature of Chinese characters. The most meaningful radicals also happen to be useful phonetic or semantic indicators, but not all radicals are, and there are a few "leftover" radicals that were created for the sake of grouping characters which can't be grouped under other radicals, such as「丨」,「丶」(zhǔ) and「丿」(piě).

To reiterate, these radicals are just shapes, and don't really mean or sound like anything to do with the characters that are grouped under them.