Pipette tips are generally well standardized between brands and broadly compatible between models. This short guide on tip fit should help you understand how to find tips from any brand that fit your pipette.
First some terminology...
Collar - The part of the pipette tip that fits onto the pipette. The diameter of the collar is what determines tip fit.
Pipette Shaft - The part of the pipette that the tips fit onto. The diameter of the shaft is what determines tip fit.
Pipette tips only come in 3 sizes:
1. 3.8mm collar - These are commonly called 10uL tips. They fit 2uL/5uL/8uL/10uL universal pipettes. Anything that is below 10uL shares this tip. This design also includes 10uL extra long, which sometimes are called 20uL as well. Some models such as Eppendorf's 20uL Research plus with a grey button use this type of extra long 10uL that holds 20uL total. Again they are 3.8mm wide, just longer to accommodate the extra volume needed for a 20uL pipette.
2. 6.1mm collar - These are commonly called 200uL tips. They fit 20uL/50uL/100uL/200uL pipettes. All these pipettes have a 6.0mm wide shaft. 300uL tips and pipettes are actually also a 6.1mm wide tip. Just like the extra long 10uL, 300uL are actually extra long 200uL tips. They have the same 6.1mm wide collar, but are longer to hold the extra volume needed for a 300uL pipette.
3. 7.4mm collar - These are commonly called 1mL or 1000uL tips. They fit only 1000uL pipettes. Some pipettes that are 1200uL (mainly multichannel pipettes) use special 1250uL extra long 1mL tips. Just like the extra long 10uL (20uL) and extra long 200uL (300uL) extra long 1000uL tips 7.4mm wide at the collar and extra long to hold the extra 200uL needed for a 1200uL pipette.
If you are looking for information on filter tips, look here.
