This might be simple or it might not...

I've got a table which stores items of equipment. Some items of equipment need servicing and they might need more than 1 type of service. So far I've come up with:

Table Name: [Equipment], PKey: [ItemID], Other fields as appropriate...
Table Name: [ServiceType], PKey: [ServiceTypeID], Description, Frequency
Table Name: [Service], PKey: [ServiceID], FKey: [ItemID],...