The 1 is a gang mold identifier. Small pieces are typically cast in multiples on the same match plate, with each individual pattern on it having a unique identifying mark (and perhaps one with no mark). These are seen with numbers as high as 7, 8 and 9. Match plates in an automated molding line are all the same size, so if patterns for 9 small pieces can be made to fit on a plate the same size that a #14 skillet's does, then it makes sense efficiency-wise to do so. The MS = Mini Skillet.