I am about to order up a set of mini hex nut drivers so I can work on my Accucraft Live Steam Shay. I’m almost certain they are all metric sizes, but one I could measure with a micrometer came out to 3.2MM. While it is not an unreasonable to think there is .2MM error in my measurement or the painted nut is a bit oversize, I just want to be sure before I order!
Jon, in my 20-something years of futzing around with Accucraft’s models I’ve found that the head sizes are approximative, to say the least. My advise is to get a set of metric, and yes they are MEANT to be metric, China is metric, just like most of the rest of the world, AND, if you can find them, a set of British BA sizes as well. There is, oddly enough, a degree of cross-over at certain sizes. BA - stands for British Association - were used for small electrical fittings and models of all kinds. The system is also one of threads, as well as bolt head sizes and nut sizes, ranging from the largest, 0, to the absolutely minute 16 BA. Taps and dies, too, of course. For certain model applications, there is also a range of bolts with one or two size smaller heads, to get a decent thread with a more scale appearing bolt head. They are all hexagon, BTW.
If you get stuck, gimme a call and I’ll send you a set. 
…and more…here’s a resplone from the mavens on the 16mm FB page - ‘Mostly metric with a few BA threads just to confuse, and ME threads on the pipe fittings.’
ME = Model Engineer standard threads. Much used in UK and anywhere else where models are built using British plans like those of LBSC - Curly Lawrence the late and great.
I can 100% guarantee that you are NOT going to find them in the US of A. And probably not Canada either. Like bangers and mash, they are a British thang.
My Accucraft locomotives are usually happy with metric.
Wiha set I have: Wiha 26592 precision metric nut driver seven piece set includes 1.5, 1.8, 2.0, 2.5, 3.0, 3.5, 4.0mm.
This set also comes with a green set of pouches to help keep them in order for about $5 or so more-worth it.
Don Howard said:
My Accucraft locomotives are usually happy with metric.
Wiha set I have: Wiha 26592 precision metric nut driver seven piece set includes 1.5, 1.8, 2.0, 2.5, 3.0, 3.5, 4.0mm.
This set also comes with a green set of pouches to help keep them in order for about $5 or so more-worth it.
Don, ALL Accucraft models are metric - and always have been. Another post on 16mm FB suggests that RH change from one system to another at the drop of a hat, but that the steam fittings are usually ME standards.
Post duplicated
Jon, I second the call for a Wiha metric tool set, and I heartily recommend this ratchet set for working on Accucraft or Aster locos:
Wiha 75965 Master Tech 65 Piece Set - ESD Handle, Mini Ratchet and MicroBits In Metal Storage Box
Not only does it include the metric nut drivers, but there are a few imperial sizes. Philips and flat screwdrivers, etc. A handle to make it easy to use it as a screw driver, and the ratchet for the stubborn stuff. I reckon that buying the Wiha metric nutdriver sets with the same capability would cost you $250 at least. I got mine from Micromark, but the Toolnut guys want $89.91.
And, get this. I thought I lost the most often used nut driver bit [figures as that one comes out all the time.] You can buy replacement tool bits from Wiha quite cheaply.
https://www.wihatools.com/bits/micro-bits/bits
Bits:
Slotted: .8, 1.2, 1.5, 1.8, 2.0, 2.5, 3.0, 3.5, 4.0mm
Phillips: #000, #00, #0, #1
Hex Metric: .7, .9, 1.35, 1.5, 2.0, 2.5, 3.0, 4.0mm
Hex Inch: .050, 1/16, 5/64, 3/32, 7/64, 1/8, 9/64, 5/32
Torx: T3, T4, T5, T6, T7, T8, T9, T10, T15, T20
Nut Driver Inch: 5/64, 3/32, 7/64, 1/8, 9/64, 5/32, 3/16, 7/32
Nut Driver Metric: 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5mm
Pentalobe: PL1, PL2, PL3, PL4, PL5, PL6
Micro Bit to 1/4" Drive Insert Bit Adapter
Wiha Micro Bits - Exact Fit Precision Machined
Micro Bits are ideal for Electronics and Optical Precision tooling
28mm Long for better handling
4mm Hex Drive
Wiha special chrome-vanadium-molybdenum tool steel
Through hardened for best wear resistance
Thank you all.
Pete, that set looks awesome and I’d consider that except I already have most of those tools. I’m missing nut drivers (or sockets) except a 3mm to where my full size set starts, I believe at 5mm.
The 7 piece Wiha nut driver set Don mentioned is the one I had in my Amazon shopping cart when I decided to ask first (https://www.largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-cool.gif)
I just ordered that set too. (https://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-wink.gif)
It’s nice. Get the pouch! But as TAC suspected, Accucraft sizes are approximate! I was removing the headlamp and bracket form an LS 2 Cyl Shay. The Metric tool did the job, but it didn’t feel snug on the fastener. It felt like it would be very easy to round it if it needed to be torqued.
The paint on fasteners makes the proper size tool feel too small. So you go to the first size larger that fits, but it is actually too large and feels that it will round out the fastener. Actually it is rounding out the paint! If you get the paint off, the proper size tool will fit. (https://largescalecentral.com/externals/tinymce/plugins/emoticons/img/smiley-wink.gif)IMHO
I did order the pouch also.
I’ve had the Wiha set for years and found there is a couple of sizes Acra uses that weren’t in the set.
Even with the paint cleaned off.