I was told on the 401K its "5329" Tax code 01 on line "2".
On a Roth IRA its rule 72t.
Plan to do the same thing in 1600 days.
Have not tried it (cant till 55) but should be able to pull the same monthly ammount out till 59 1/2, 10% penality free.
Again, still learning,
Exception Codes for Form 5329 Line 2
The following exception codes are to be used for Form 5329 Line 2 to inform the IRS that part or all of your retirement withdrawal is not subject to the early withdrawal tax penalty. The following exception codes are found in Instructions for Form 5329
(PDF), pages 2 and 3.