On the segwit page there is a reference that the "feffffff" is the "sequence". What does the "sequence" represent in relation to what? Does it always have to be "feffffff"? What happens if it's "feffffff" instead of "ffffffff"? Does it help anything, does it hurt anything? Am I just fine using just "ffffffff" instead of "feffffff" What other options are there and what do they mean?

1 Answer 1


Sequence is part of any input, before segwit as well. feffffff is the hexadecimal number 0xfffffffe because the bytes need to be reversed. This sequence number, as per BIP 125, is because:

Wallets that don't want to signal replaceability should use either a max sequence number (0xffffffff) or a sequence number of (0xffffffff-1) when then also want to use locktime;

So this sequence number uses the locktime but does not signal replaceability

If instead you used 0xffffffff, the sequence number would have no effect on the transaction.

If you don't know what locktime is, check out this question: What is Bitcoin's locktime feature exactly? How can it be used?

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    So, "What [actually] happens if its 'feffffff' instead of 'ffffffff'?" "Does it help anything, does it hurt anything? Am I just fine using just 'ffffffff' instead of 'feffffff'?". and what does "locktime" mean?
    – Mine
    Aug 18, 2017 at 21:01
  • Use feffffff if you want to use the locktime functionality in your transaction. Asking what locktime is is a distinct question, should not be a comment bitcoin.stackexchange.com/questions/43067/… Aug 18, 2017 at 21:20
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    I would put forth that that is not necessarily the case. Thank you for the update to your answer and the link.
    – Mine
    Aug 18, 2017 at 22:48

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