Screws - plain shank or 100% threaded?

headey · Post by **headey** » Mon Dec 13, 2021 6:48 pm

This topic must have been covered before, so apologies in advance, but why is it becoming difficult to find traditional screws with 1/3 plain shank and 2/3 thread?
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When I did O'Level woodwork way back in the early 70s, screws had the top 1/3 of the shank plain. I was taught that this was to ensure that the top piece of wood could move freely and thus be pulled down firmly to the bottom piece that contained the threaded part of the screw. Indeed, I was even taught to put a small countersink on the underside of the top piece of wood so any raised grain would not force the two pieces apart.

These days, it seems that many screws have a thread that runs up to the head. Unless the top piece of timber has a sufficiently large clearance hole, it is possible for the two pieces of wood to screw together with a gap between them. Indeed, this happens quite frequently if the timbers move while screwing.

Can anyone explain this conundrum? What is the theory of the 100% threaded shank?

arco_iris · Post by **arco_iris** » Mon Dec 13, 2021 7:31 pm

An extremely complicated subject, for instance see wikipedia.

From a DIY perspective, I'd hazard an opinion that screws with shanks need pilot holes to start them and fully threaded are "self-tapping", no pilot needed.

I too did 'O' Level Woodwork (Grade 1) in 1973 but don't remember that.

dewaltdisney · Post by **dewaltdisney** » Mon Dec 13, 2021 9:05 pm

I cannot remember the last time I used a tradional slot head shanked screw, the common self tapping screws suit cordless. Most developments in woodwork are to save time and driving screws, nailing plus the range of adhesives are all designed to speed up work. Even though you may need pilots for some woods close to the ends to avoid splitting out or for hard woods that would bind the screw and possibly damage the screw head, mostly you can drive screws in without a pilot.

My antique dealer friend buys speacilly made woodscrews for restoration work and this is where the the screw is deliberately made off centre to copy early forms of screw making.

DWD

headey · Post by **headey** » Mon Dec 13, 2021 9:37 pm

I too did 'O' Level Woodwork (Grade 1) in 1973 but don't remember that

You swot! You and I are exact contemporaries, as I also did my o'levels in 73. I only managed Grade 2 (Interestingly, I had an idea other exam boards used A, B, C grading. Did all exam boards use the same grading system or just the ones we took?)

dewaltdisney wrote: ↑Mon Dec 13, 2021 9:05 pm I cannot remember the last time I used a tradional slot head shanked screw

Nor can I. I don't think the head type is particularly relevant, as I have Pozi head screws with a plain shank. As for the self-tapping nature of the thread not requiring a pilot hole, that sounds plausible. Even so, does the need for self-tapping require the thread to run all the way to the head?

arco_iris · Post by **arco_iris** » Mon Dec 13, 2021 9:53 pm

That's one of the ways that old furniture can be dated - if it has pozidrive or cross headed screws, it can't be very old!

Pozidrive is generally European whereas Philips is generally North American (and automotive). Both suit power tools. To a degree.

Us old-school can deal with both, if we can source the correct bits. I've recently restored a toolbox made by hand by the wife's grandfather, a shipwright, in we think the 1920's. Very, very carefully removing and reusing where possible the original screws. For the brass plaque on the lid, I was able to obtain some period screws off fleabay.

dewaltdisney · Post by **dewaltdisney** » Mon Dec 13, 2021 10:02 pm

Yes, the shank would bind on the threaded cut not being wide enough. I did O level woodwork in 1967, I built a wooden box, it was shite. The dovetails are so bad you can see daylight. The irony is I still have it, I use it as an ammunition box as strangely it holds two columns of 12 gauge shotshells to stack.

DWD

arco_iris · Post by **arco_iris** » Mon Dec 13, 2021 10:17 pm

DWD!

I made a fibreglass teatray AND a small table, both of which I still have (following the demise of my parents, the items came back).

headey wrote: ↑Mon Dec 13, 2021 9:37 pmYou swot! You and I are exact contemporaries, as I also did my o'levels in 73.

I would not use the term 'swot' as I really detested school, it was just that I had a very practical bent (that's why I'm on ultimatehandyman). I went on to be a motor engineer in the days when things would be refurbished and repaired, not, as now, simply replaced by a 'fitter'. So I understand bolts, set screws, shanks and heads.

dewaltdisney · Post by **dewaltdisney** » Tue Dec 14, 2021 12:12 am

I remember we had a Stanley Plough plane at school. It was coveted by the teacher and we were only allowed access to it by begging. When I finally convinced him I needed it for a rebate I found out it was virtually impossible to get a right angled rebate as it wandered and tilted, I had to straighten the rebate with a chisel. I never bothered with it after that. God bless routers

DWD

Grendel · Post by **Grendel** » Tue Dec 14, 2021 6:00 pm

I was taught the bit about countersinking the underside of the timber too and it's something i do at times. It can be irritating at times using fully threaded screws when they force the two pieces apart but to be fair drilling a pilot or clamping the two pieces together seems to solve the problem and it doesn't really bother me that much. My old drill had seen better days and i brought the dewalt twinpack of a drill and impact driver and that has probably got me more back into the habit of pilot hole and countersinking as i don't have to keep faffing about changing bits. Funnily enough today i used some slotted four inch stainless screws and i piloted and put them in with the impact.
DWD I have a plough plane and do still use it occasionally . I find it useful for small runs of tongue and groove and have the matching wooden tongue cutter plane. Sometimes just as quick as messing about with the router. Saying that i did use the router today for some grooving on a frame. I also used my hand rebate plane to clean up some glazing bars I'd cut with the power plane.
Incidentally i gave up woodwork at school along with history so no o levels or cse's or whatever. Left school and started an apprenticeship and did my city and guilds , worked on historic building restoration and also have made numerous pieces of medieval furniture for the re-enactment scene.

fin · Post by **fin** » Tue Dec 14, 2021 6:51 pm

ive litterally just got a one of those howdens reisser screw boxes... the shorter lengths have fully threaded screws and the longer ones are part threaded. so 60mm and below are fully threaded and above are part threaded

fin · Post by **fin** » Tue Dec 14, 2021 6:53 pm

i also bought the boxes of screws at screwfix that were on special the other week.... ill check those as was going to top up the empty screwbox that ive got.. sure that the goldscrews from screwfix follow the same part and fully threaded sizes th same as the reisser screws

Grendel · Post by **Grendel** » Wed Dec 15, 2021 8:21 am

I did look at what i've got . I do have some 3" and 4" fully threaded but generally i'd say fin is right , part threaded is more common in the larger screws. The4" I was using yesterday were threaded to about an inch from the head. Brass screws seem to follow the pattern of being pretty much all part threaded if my stocks are anything to go by. If I 'm honest for most applications I don't feel it makes any real difference.