Snap fastener with a differentiated buttoning and unbuttoning effort female part

A snap fastener, of a type comprising a female part (2) including a circular ring-shaped spring (11, 11a, 11b) having a circular inner hole (20) and a male part (4) having a male part stem (5) for engaging with said circular ring-shaped spring made of plastic material, said circular ring-shaped spring (11,11a,11b) comprises a slanted wall beveled portion (18) on said inner hole (20) that facilitates the engagement of the snap fastener male part (4) with said female part (2), characterized in that said snap fastener further comprises engagement means having different resistance to with differentiated buttoning and unbuttoning efforts, between said stem (5) and said circular ring-shaped spring (11,11a,11b), said engagement means comprising a chamber (10, 10a, 10b) provided inside said female part (2) for housing said circular ring-shaped spring (11, 11a, 11b), said chamber (10, 10a, 10b) further having a longer chamber shoulder (12, 12a, 12b) on a buttoning side of said female part (2), said longer chamber shoulder having a first length (L1) longer than a second length (L2) of a corresponding shorter chamber shoulder (13, 13a, 13b) arranged on an opposite side to said buttoning side of said female part (2), said longer chamber shoulder (12, 12a, 12b) provides said circular ring-shaped spring (11, 11a, 11b) with a corresponding shorter spring free portion (15, 15a, 15b) as compared to a corresponding longer spring free portion (14,14a,14b) of said circular ring-shaped spring (11, 11a,11b) whereby said shorter spring free portion (15, 15a, 15b) of said circular ring-shaped spring (11, 11a, 11b) provides an enhanced resistance against unbuttoning, and said circular ring-shaped spring (11, 11a, 11b) having a corresponding longer spring free portion (14, 14a, 14b), which deforms as said stem (5) engages said female part (2) and facilitates engagement of said female part (2) by a longer length of said longer spring free portion (14, 14a, 14b) of said circular ring-shaped spring (11, 11a, 11b.