For a quick, inexpensive solution I'd recommend one of two things:
1. Ask your string maker to reserve to the exact nock you want to shoot. I don't know what exact nock you are shooting now, but for those GT Pro Hunters imagine it's the GT GTO nock fit into their accu bushing. That center serving should be finished to a finished diameter equal to that nock, which is .114. Ideally, the string maker has the nock on hand because final fit is more of a "feel thing" than meeting specs to the thousandth of an inch. The stringmaker can grow the center serving by adding a thicker serving material -- say going from Halo .014 to Halo .018 for example. I realize that sending a string back is somewhat annoying to you and the stringmaker, but frankly string makers should be asking folks up front what nock they want to shoot / what finished center serving diameter they are after. Not doing so is askin to selling someone tires without asking them what size they need.
2. Get new nocks. Again, the nocks on your Gold Tip Pro Hunters (if they are what came with the arrows) should be the GT GTO nock which is a .166 inch diameter nock in GT's accubushing. That's a great nock that works well with a center serving diameter size of .114 inches give or take .002 but no more or less.
If you get new nocks, some good ones to consider are:
- Easton Microlite 4mm (these are about a .107 inch throat so are rather snug compared to the GT GTO)
- Beiter Pin Nocks. You'll want to look at either the Beiter Hunter #1 (.103 groove) or Beiter 1 Small (.106 groove). These are excellent German-made nocks and available at Lancaster Archery online. You'll want to upgrade the bushing to a .246 pin bushing. These are available from Gold Tip, Altra, and Top Hat.
One of those three nocks should work. If it doesn't, pick the nock you want to shoot and reserve. The best nocks out there are Beiter, Easton, and some Gold Tip in that order.
Folks typically recommend reserving, and while that's a long-term option, you aren't set up to do that quite yet to do it well you'll want a serving jig and a few serving sizes which will cost you some money. If you are worried about a $15 pack of nocks, then get ready to spend $100-200 to get set up to serve.
One last word on nock size -- nocks come in all sizes and stringmakers make all sorts of finished diameters! Those 0.88 and 0.98 dimensions are published numbers from Easton for their "small throat" and "large throat" nocks respectively, but those numbers don't always align with true measurements on their nocks.
A great resource to plan our nock purchases and string builds is a piece by OCD Strings called
"What Nock and I Shooting". Highly educational and actually inspired me to buy
this set of pin gauges to measure my own nocks and order strings more accurately. Julie lists all the common nocks on her blog post, and if there's one on there you don't see ask me and I can see if I have one on hand to measure.
PS, OCD Strings also has a
good blog post on ideal nock fit for those reading who are going through something similar as the OP.
Good luck!