PSE: 38mm (1.5″)
Planed timber is often referred to under a variety of different terms, PSE (planed square edge), PAR (planed all round), or the more straightforward term, smooth.
Planed timber is often used where the finish of the timber is likely to be on display, hence where a smooth finish will be important. It is worth noting that the planing process takes a thin layer of material off each side of the plank. This means the finished size will be slightly smaller than what is listed.