Schedule 40 Steel Pipe Nipple, 3/8-18 Male NPT, 6.00 Inch Long

Standard 3/8-18 NPT threading on both ends, so it'll mate up with any fitting or port cut to that same spec. No thread sealant comes applied to it, so you'll want to add your own tape or compound before running it in. Schedule 40 wall thickness holds up well in typical industrial hydraulic connections setups, and the black finish gives it some added resistance to corrosion over bare steel.

While the wrench size isn't specified, this is a standard 3/8-18 male NPT fitting, so a wrench appropriate for that size should work fine.