Funnel structure for oil case

A funnel, comprising:

• a funnel body, which has a top surface that is made inclining at a predetermined slope and has a circumferential wall forming two opposite cut-offs for helping stabilizing an oil bottle in an up-side-down condition for pouring oil, the funnel body having a bottom forming a first joint tube projecting therefrom, the first joint tube has a circumferential surface forming a first key;
• an extender, which is of a hollow tubular configuration and has a bottom end forming a second joint tube projecting therefrom, the second joint tube having a circumferential surface forming a second key, the extender having a top end forming a first joint bore, the first joint bore having an inner circumferential surface forming a first keyway, the first joint bore of the extender selectively receiving the first joint tube of the funnel body therein with the first key fit into the first keyway for rotatably fixing;
• and
• a conic cap, which is of a hollow configuration and has a top end forming a second joint bore, the second joint bore having an inner circumferential surface forming a second keyway, the second joint bore selectively receiving the second joint tube of the extender with the second key fit into the second keyway for rotatably fixing, the conic cap having a bottom end forming a round tube projecting therefrom, the round tube having an outer circumferential surface forming opposite projections, whereby the projections are adapted to move through notches formed between inward-projecting flanges formed inside an oil feeding port of an oil case and the conic cap is rotated to have the projecting located below and engaging the inward-projecting flanges of the oil feeding port for secure retention of the conic cap in the oil feeding port.