Sesenta –sixty in Spanish— was the name of a limited edition of the slim Pilot Capless. The records say that there were three series of 400, 100 and 100 units in marbled brown, red and green, respectively, released in June 2007. There is also a generalized idea that these Sesenta pens were the beginning of the model Decimo (tenth in Spanish), the non-limited version of the slim Capless. However, those same records show that there was a Decimo pen in pink in November 2005, this predating the first Sesenta.
Another general idea is that the nib-feed-ink deposit set of all Capless pens can fin in any of the models made after 1990: regular Capless, slim Decimo/Sesenta, and Fermo. But I have found that golden colored nibs, either made in gold or in steel, do not fit well in the slim versions. These nibs seem to be slightly thicker at some point and the push-pull operation is not smooth. This is the case with two pens—a Sesenta and a Decimo— and with three different nibs—two gold plated in steel, and one 18 K in gold.