You must have two halfbacks and two hookers, so these two must be considered as third-choice options for the All Blacks

My friends in the front-rowers club – many and learned as they are – tell me you should always choose your tighthead prop first and then your reserve tighthead prop when selecting your match-day 22 or 23.

They may be right, but there are also two selectorial non-negotiables: you must choose two halfbacks and two hookers in your squad. They are, props aside, the most specialised positions on the field. You can get away with non-specialists on the bench and versatility is indeed encouraged, especially in the backline and among those who can suit up in the loose forwards and locks.

So when the All Blacks selectors sit down to name their 31-man Rugby World Cup squad, they will need a No 3 No 2 and a No 3 No 9, if you follow me.

Unless there is a massive shift in thinking or an injury crisis, the halfbacks will be Aaron Smith, TJ Perenara and Te Toiroa Tahuriorangi. The first two speak for themselves. Tahuriorangi, however, has this week been thrust into the limelight by virtue of the fact that Brad Weber, a one-test All Black in 2015, has played so well for the Chiefs, for whom he is also stand-in skipper.

Colin Cooper clearly backs Weber’s leadership and form, despite the fact that he promoted ‘Triple T’ at Taranaki as far back as 2015. The numbers are stark. Weber has scored four tries in 10 outings and racked up 689 Super Rugby minutes. Only five Chiefs have more minutes and yet Weber is in a job-sharing position. Tahuriorangi, by contrast, has made two starts, scored two tries and compiled just 242 minutes. That should not be enough to be a prime RWC contender. But the selectors have decided he is the future and has more upside than Weber, and the Crusaders duo of Bryn Hall and Mitch Drummond, both of whom have been fringe All Blacks.

Tahuriorangi’s plight is not caused by poor form, but rather the dynamism of Weber behind a pack that has missed Sam Cane, Brodie Retallick and front-row stability for large tracts of the season.

There may be some direct phone calls between Steve Hansen and Cooper in the coming weeks if the Chiefs drop out of playoffs contention and perhaps even if they do not drop out of playoffs contention.

The hooker situation is rather cloudier. Codie Taylor is clearly the best hooker in the land, and Dane Coles should be his back-up, but is labouring with injury and has made just five appearances for the Hurricanes. Nathan Harris is the top rake at the Chiefs, but, despite showing some silky touches around the field in 2019, has yet to command an All Blacks position, though he has 20 tests’ worth of experience to call on.

Falling off the pace are Ricky Riccitelli and James Parsons, while the admirable Ash Dixon has never got a look-in other than at Maori All Blacks level.

Step forward Liam Coltman, four tests since 2016, but always the third or fourth choice at best. The 29-year-old is playing his way into the All Blacks squad. Coltman has been the benefactor of the Highlanders’ lineout drive but, more importantly, he is leading the pack from the front along with Tom Franklin.

There was a time when Coltman was the Aled de Malmanche of New Zealand rugby – good rugby player, but struggling to hit his lineout targets, having switched from prop. But Coltman has tidied that up and is making a solid case that he is All Blacks material. Furthermore, dependent on how Coles bounces back, he might well be wearing the No 16 jersey in black on a far more permanent basis.

Third-string hookers and halfbacks at a Rugby World Cup are more than just bit-part players. They will start at least one match and have to train the house down, knowing injury could swiftly thrust them back into the spotlight. Taylor was the third wheel in 2015, and Corey Flynn was in that slot back in 2011.

Perenara found himself in that unfamiliar role as Tawera Kerr-Barlow leapfrogged him in 2015, while Jimmy Cowan, despite his yeoman service in 2008-10, was overtaken by Andy Ellis in 2011.

We are four months out from Japan 2019, so there is time for a change of thinking, but those specialist roles should never be taken lightly.

Ryan Crotty ahead of Stormers’ clash: