I got my hands on an old PC heat sink, intel 775 I think.

Will this fit on my i5-8400 8th gen?

And if it does, what side does it go on?

The copper core is indented on one side and sticks out the other

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  • The side with the copper protruding from the aluminium fins goes on the CPU, otherwise it could not make contact. Normally, these heatsinks come with a mounting mechanism. This -missing- part determines which socket it can fit. One could certainly cobble together a solution to make this work on Socket 1151. It is still missing a fan though, which would normally be attached to / a part of the plastic mounting mechanism. Overall, not worth the effort compared to working solutions starting at 5$ plus shipping.
    – user13807
    Apr 9, 2020 at 21:55

1 Answer 1


It isn't going to fit.

The LGA 775 socket CPUs are a different form factor, 37.5mm square, than the i5-8400 which uses an LGA 1151 socket.

The distance between the screw-holes for the heatsink of an LGA 775 is 72 mm. Such heatsinks are not interchangeable with heatsinks for sockets that have a distance of 75 mm, such as the i5-8400 which uses the LGA 1151 socket.

  • 1
    Thanks for the clear answer, I asked on Facebook groups, and just got a whole bunch of snotty millenial kids giving me different opinions on this! Great to get an answer from a guy who knows what he's talking about, cheers! Apr 10, 2020 at 2:12

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