JT Realmuto swings an Old Hickory custom Maple bat, the JTR1 model. The JTR1 bat has a DP15 (S318) barrel with Nolan Arenado’s NA4 handle, which is a “shovel” knob.
Anyone who wants this bat will have to make a custom order with Old Hickory, as Realmuto’s model is not available otherwise. Realmuto’s bat has an ebony barrel, black handle, and he cups the end.
A close alternative might be the DP15, available at OldHickoryBats.com.
JT Realmuto’s bat measurements: 34/31