for switch insert ref.-no.: 501 U, 502 U, 503 U, 506 U, 507 U, 501-20 U, 506-20 U, 507-20 U
for push switch insert ref.-no.: 502 TU, 506 TU, 507 TU
for push-button insert ref.-no.: 531 U, 532 U, 533 U, 533-2 U
for multi push-button insert ref.-no.:
531-41 U (not metal versions)
