The spelling of the word "peens" may seem confusing to some, but it's actually quite simple. The word is the plural form of "peen", which is a noun used to refer to the hammerhead opposite the main hammerhead on a double-faced hammer. The IPA phonetic transcription for "peens" is /piːnz/. The final "s" is pronounced as a voiced "z" sound, as is typical in English when a noun is pluralized with an "s". So, the correct spelling for more than one peen is "peens".
The word "peens" is a plural noun form of the word "peen". The etymology of "peen" can be traced back to Middle English, where it originated from the Old English word "pēne", meaning a chisel or an (architectural) wedge. It likely derived from the Proto-Germanic word "spanō", which referred to a spear or pointy object. The word gradually evolved in Middle English to "peine" and then to "peen", where it took on its current form. In the context of tools like hammers, the peen specifically refers to the end opposite the striking head, which can have various shapes depending on its purpose.