By now you realize your Takeuchi TL12-v2 track loader has quite a few serial break options for the undercarriage parts. Takeuchi completely changed the undercarriage type and rubber track guiding system at 412000578. This category is designed to navigate the parts selections for the later serial numbers. Read the descriptions but please check your parts manual and owners manual for specific part numbers to verify.
The 412000579 serial break is when Takeuchi changed over to a smooth outside guide rubber track with sixty drive links and a drive sprocket that has sixteen drive teeth. The idler is specific to this model and this exact serial range.