How does a converter dolly physically connect to the trailer in front of it, compared to how the next trailer connects to the dolly?

49 CFR 383.115(a) ("Procedures for assembly and hookup of the units"); AAMVA CDL Manual Section 7.2.1 "Coupling Twin Trailers" (converter-gear definition, Figure 7.1, and coupling steps), p. 7-2

Recognizing that a dolly uses two different coupling mechanisms, front and rear, explains why dolly-specific inspection items like pintle-eye seating and pintle hook latching exist on top of the usual fifth wheel checks.