Kind:

21mm ordinary 21 * 8Ω * 0.25W

21mm environmental protection 21 * 8Ω * 0.25W

27mm thin magnetic ordinary 27 * 8Ω * 0.25W

27mm common 27*8 Ω * 0.25W)

27mm environmental protection 27 * 8Ω * 0.25W

29mm ordinary 29 * 8Ω * 0.25W

29mm iron shell 29 * 8Ω * 0.25W

29mm environmental protection 29 * 8Ω * 0.25W

29mm large magnetic common 29 * 8Ω * 0.25W