Available four chars domains with results in the WayBack Machine

As usual, all of them were available at time of posting.
Remember that you can always use the domain checker in the right sidebar to verify availability at time of your visit.

YS4F.COM
LVIP.NET
N999.NET
JKTX.NET
HKOB.NET
DYHZ.NET
FGZX.NET
B135.NET
HPZX.NET
68FX.COM
TAB8.COM
IE08.COM
UEBP.NET
YHWL.ORG
66ZQ.COM
669K.COM
HFDZ.NET
V98V.COM
KYGJ.NET
52GW.NET
LMA0.NET