New buttons: New buttons are Muktzah on Shabbos. However, it is disputed as to which level of Muktzah they contain. Some Poskim rule that they are MM”I [Muktzah Machmas Issur, or Keli Shemilachto Lissur] and thus may be moved to use their space or for a permitted use. Other Poskim however rule that they are MM”G [Muktzah Machmas Gufo] and may thus not be moved at all.
Are buttons that have fallen off clothing Muktzah? Some Poskim rule that buttons that have fallen off a clothing are not Muktzah on Shabbos. Other Poskim rule that if one is particular to use this specific button to resew onto the original clothing it fell from then it is not considered Muktzah. If however one is not particular to resew it to the garment it fell from, then the button is considered MM”I. Other Poskim rule that only if the button is fit to cover a vessel [such as a bottle] does it retain its Non-Muktzah status. Admur does not hold like this later opinion.
 Ketzos Hashulchan 109 footnote 8
The reason: As that they have never yet been attached to a vessel, and only those items which have been attached to a vessel retain their vessel status when detached. [Ketzos Hashulchan ibid]
 Ketzos Hashulchan ibid
 The reason: As the buttons are considered a vessel being that they are designated for a specific use. [Ketzos Hashulchan ibid]
 Minchas Shabbos 88/2
 The reason: As they are not yet considered a vessel. [Minchas Shabbos ibid]
 Minchas Shabbos ibid; brought in SSH”K 15/68 and footnote 221, however there he concludes that it is proper to be stringent like the third opinion that will be brought.
 The reason: As they are still fit to be returned to their original clothing. [See Admur 308/34; Michaber 308/8; Shabbos 122b; Rashi on Shabbos ibid; Taz 308/8; P”M 308 M”Z 8; M”B 308/35]
 Ketzos Hashulchan ibid
 The reason: As the entire allowance that detached parts do not become Muktzah is based on that one intends to return the item to its vessel. [See Admur 308/34; Michaber 308/8; Shabbos 122b]
 Meiri; SSH”K 15/68 footnote 222 in name of RSZ”A rules that it proper to be stringent like this opinion; Beir Moshe 6/87
 As the later opinion is based on the Meiri who learns that the allowance by detached doors is based on that they are fit to be used to cover vessels. Admur however writes that the reason is because they were once attached to the vessel and are fit to be returned, and entirely omits this concept that they are able to cover a vessel. Thus, according to Admur, as well as Rashi on Shabbos ibid; Taz 308/8; P”M 308 M”Z 8; M”B it is irrelevant what the size of the button is.