In the ring of the needle cylinder two types of sinkers are provided; a sinker (53) with a high nose (53A) for the terry yarn, and a sinker (51) with a low nose (51A) for the base yarn; a high yarn guide feeds the terry yarn over the sinker (53, 53A), and a lower yarn guide feeds base yarn at a lower level than the level of the surface (53A) of the nose of the sinker (53); a fixed annular sinkers housing (55, 55A) controls the high-nosed sinkers (53) with an area of centrifugal retraction that is substantially symmetrical with respect to the yarn guides; an angularly mobile annular sinkers housing (59) controls the low nosed sinkers (51), with a cam (57A) having an apex pointing outward, which alternates - with each reversal of the motion of the needle cylinderbetween two positions that are substantially symmetrical with respect to the yarn guides, in order centrifugally to retract the low-nosed sinkers (51) each time in proximity to the stitch-forming area, occurring after the feeding position (A).