Protective device for an electrical connection of an on-board device of a bicycle, said electrical connection comprising a first connector electro-mechanically coupled with a second connector along a longitudinal axis, the protective device comprising: - a first protective element of said electrical connection; - a second protective element of said electrical connection, said second protective element being arranged on a diametrically opposite side of said first protective element with respect to said longitudinal axis when said first protective element and said second protective element are stably coupled with said electrical connection; - coupling means (50, 50a, 50', 50'a) for removably coupling said first protective element with said second protective element, wherein said coupling means (50, 50a, 50', 50'a) are made in one piece with said first protective element and second protective element, characterized in that said first protective element and second protective element are symmetrical with respect to a longitudinal middle plane of the protective device, and in that said coupling means (50, 50a, 50', 50'a) are formed on axially opposite free end portions (20, 20a, 20', 20'a) of said first protective element and second protective element, wherein the coupling means (50, 50') formed on one (20, 20') of the free end portions (20, 20a, 20', 20'a) of one of said first protective element and second protective element are different from the coupling means (50a, 50a') formed on the other (20a, 20a') of the free end portions (20, 20a, 20', 20'a) of the same protective element (10, 10') and wherein one (20, 20') of said free end portions (20, 20a, 20', 20'a) of one of said first protective element and second protective element comprises, in a cross section thereof, a conical outer side surface portion (34, 34') and an undercut outer side surface portion (35, 35') arranged in a radially inner position with respect to said conical outer side surface portion (34, 34'), and wherein one (20'a, 20a) of said free end portions (20, 20'a; 20a, 20') of the other of said first protective element and second protective element comprises, in a cross section thereof, a conical inner side surface portion (34'a, 34a) and an undercut inner side surface portion (35'a, 35a) arranged in a radially outer position with respect to said conical inner side surface portion (34'a, 34a). - a first protective element of said electrical connection; - a second protective element of said electrical connection, said second protective element being arranged on a diametrically opposite side of said first protective element with respect to said longitudinal axis when said first protective element and said second protective element are stably coupled with said electrical connection; - coupling means (50, 50a, 50', 50'a) for removably coupling said first protective element with said second protective element, wherein said coupling means (50, 50a, 50', 50'a) are made in one piece with said first protective element and second protective element, characterized in that said first protective element and second protective element are symmetrical with respect to a longitudinal middle plane of the protective device, and in that said coupling means (50, 50a, 50', 50'a) are formed on axially opposite free end portions (20, 20a, 20', 20'a) of said first protective element and second protective element, wherein the coupling means (50, 50') formed on one (20, 20') of the free end portions (20, 20a, 20', 20'a) of one of said first protective element and second protective element are different from the coupling means (50a, 50a') formed on the other (20a, 20a') of the free end portions (20, 20a, 20', 20'a) of the same protective element (10, 10') and wherein one (20, 20') of said free end portions (20, 20a, 20', 20'a) of one of said first protective element and second protective element comprises, in a cross section thereof, a conical outer side surface portion (34, 34') and an undercut outer side surface portion (35, 35') arranged in a radially inner position with respect to said conical outer side surface portion (34, 34'), and wherein one (20'a, 20a) of said free end portions (20, 20'a; 20a, 20') of the other of said first protective element and second protective element comprises, in a cross section thereof, a conical inner side surface portion (34'a, 34a) and an undercut inner side surface portion (35'a, 35a) arranged in a radially outer position with respect to said conical inner side surface portion (34'a, 34a).