Key Knob 4 for inch B inch Size RAM® Pin-Lock™ Security Knobs The RAP-S-KEY3-4U replacement key knob is compatible with the RAP-S-KNOB3-4, RAP-S-KNOB3-4U and RAP-S-KNOB3/RAP-S-KNOB3U mixed combination security knobs that contain the 4 node security pattern. Please verify the node security pattern on your security knob before purchase.