I see in the Avi Ezri of Rav Shach that he equates mashkon and eravon, and he has good reason to do so since the Gemara itself (bava metzia page 48) asks from one to the other and that implies that they are the same. However, the case of mashkon is a guarantee for a loan and eravon is a guarantee for a sale, and the Rambam does not equate them. The eravon guarantees the whole sale like R Yochanan said in Bava Metzia 48. A mashkon is for a loan or other obligations. There the mashkon guarantees just the amount parallel to its worth (as per Laws of Loans chapter 13 law 4)---------------------I see in the אבי עזרי of רב שך that he equates משכון and עירבון, and he has good reason to do so since the גמרא itself (בבא מציעא מ''ח ע''ב) asks from one to the other and that implies that they are the same. However, the case of משכון is a guarantee for a loan and עירבון is a guarantee for a sale, and the רמב''ם does not equate them. The עירבון guarantees the whole sale like ר' יוחנן said in בבא מציעא דף מ''ח. A משכון is for a loan or other obligations. There the משכון guarantees just the amount parallel to its worth (as per הלכות מלווה ולווה chapter 13 הלכה 4)