Straight threaded o-ring ports are used on all II MUCH fuel system products. This port is common in many high quality automotive aftermarket products but adapters are often described by many different names. For instance, in just one major online catalog its described as "straight cut o-ring", "-6 AN O-ring", "AN to straight cut", and o-ring boss (ORB). Given the variety of fittings available in major online catalogs it can be daunting to find these otherwise ubiquitous adapters.
The above adapters are both -6 AN male, but the one on the left adapts to 1/8" pipe thread and the one on the right -6 straight thread o-ring.
In this blog post we will discuss the SAE standard that accurately describes this port, benefits of this port vs a NPT port, and search phrases.

 The Society of Automotive Engineers standard J1926 describes the dimensions and requirements for o-ring ports and machine shops will commonly create this port with an all in one cutter that creates all of the features in one pass. 

The o-ring port on the bottom of a II MUCH VSB vent system (P/N 200025)

Leaks are less likely with the o-ring port but if they do happen they might be attributed to any of the following

• Worn cutters used to create the ports and lack of sufficient quality program -- this is more common with the knockoff parts often found being sold at a fraction of the price of original. 
• O-ring improperly installed resulting in a cut or pinch.
• Improper torque. 
• Threaded portion longer than SAE specification resulting in the fitting bottoming out in the port before the o-ring can fully compress.

The jam nut on the o-ring port adapter will allow the hose assembly to be rotated in any orientation desired for optimal packaging. This is not possible with a NPT adapter as its final position is somewhat random and NPT ports often get stripped in an attempt to achieve optimum clocking.

Per SAE J1926:

"The ports shall be specified by SAE J1926-1 and the thread size (without UNF or UN and 2B designation), separated by a
colon, for example SAE J1926-1: 1⁄2-20."

In theory, the adapter on the bottom is SAE J1926-1 9/16-18, and the one on the top is SAE J1926 7/8-14, but using the proper SAE name will often turn up far less results when searching through an online catalog because the SAE naming convention is not followed much.
To search for the J1926-18 the following seems effective:
"straight cut o ring fitting" and "-6"

While "o-ring boss" and "ORB" seem less so.

Here's some examples from Summit Racing if searching doesn't get you there.

9/16-18 O-ring port to -6 male AN

Or just click on this image for a bunch of options for the Summit Brand