F15A Cab Rope Lashing Points
 

Hi all,
my F15A is slowly going back together and I am refitting the rope lashing points on the rear corners of the cab. The odd little anchor nut plates inside seem to 3/16 inch thread, but the holes in the lashing point are much larger, more like 5/16. I have lost the original screws, so I don't even know what sort of head the screws should have.
My questions are:
1. what size screws should be fitted? Maybe my lashing points are not original.
2. What sort of head should the screws have? Countersunk or round head?

thanks

Lashing cleat screws
 

Hi Eric,

Going by mine, they should be 1/4-20 UNC Flat head countersunk slotted screws about 3/4" long. They are the same as the screws that hold the floorboards down.

Some of these cleats were retrofitted and used 2 separate nuts on the inside of the cab. Later versions had a plate with two threaded bosses to accept the above screws, spot welded to the cabin lower back.

Cheers,

Jacques

Further to lashng cleat screws
 

Hi Eric,

Just to add the attached photo showing the aforementioned plates that are spot welded to the rear of the cabin. I had an earlier cabin where there was no plate but the cleats were just attached via the screws and nuts.

Have noticed often that WW2 fastener head sizes are substantially larger than those on currently made fasteners. Case in point is those screws. Compared to a modern screw with the same threads, the countersunk head is substantially larger on WW2 screws so if you can scrounge a couple from and old floorboard you will find they fit the cleat perfectly.

Cheers,

Jacques

Is this a unique Australian feature?

I have noticed that many Australian-built cabs feature Whitworth fittings, oddly often right alongside SAE threads. 1/4" UNC and 1/4" BSW are both 20tpi, but the UNC hex is 7/16" and the 1/4"W is 0.525".

Whitworth Hex sizes were oversized in relation to the thread diameter by current trends, but in 1940 an austerity measure was introduced with War Emergency B.S. 916 : 1940 to conserve steel. This had the effect of reducing bolt hex sizes by one smaller spanner size for the same thread. For 1/4" BSW, the old hex of 0.525" became 0.445", which is very close to 1/4" UNC (7/16" = 0.438"). Wartime BSW threads are very easy to mistake for UNC due to this close similarity of Hex sizes. While these measurements relate to Hex headed bolts, the same applies to countersunk screws.

Whitworth vs SAE
 

Hi Tony,

Yes, I noticed the various Whitworth screws as used on my truck also, mainly on the Holden built body and Australian cab but perhaps I was not clear in my comment.
I was referring to the actual head height of many of the SAE screws and nuts used on the truck. Most are much higher than the currently manufactured ones. See the attached example of two 3/8 UNC screws a commonly used fastener on the truck. New one on the top. Both use 9/16 AF spanners but the height from the bottom of the head to the top of it is higher on the original WW2 manufactured one.

Cheers,

Jacques

I think the thick headed SAE bolts you are describing are also known as "heavy hex head bolts", described at http://www.mcmaster.com/#standard-cap-screws/=13bs90h and drawn at http://www.mcmaster.com/#92655a331/=13bs912
They aren't cheap, but they seem to exist if you need them.

Hi Eric,

Just getting back to the original questions:

See attached photo.

The cleat does have substantially larger holes than the screws passing through them. Below the cleat are the two different size heads on 1/4 UNC/Whitworth screws. As can be seen the newer screw has a smaller head than the WW2 floor screw on the left. Having said that, upon checking my spare cleat the newer type screw will hold the cleat quite adequately even though the diameter at the top of it is smaller than the older type screw.

These cleats are invariably broken when found on the trucks. I think they were just standard hardware items of the day as used to secure awnings on buildings etc.

Cheers,

Jacques

Lashing Points
 

Hi all,
thanks for the information. My cleats are exactly the same as the photo that Jacques has posted. And my truck has the spot welded anchor nut plate. I agree that the modern screws have smaller heads. I had a great deal of trouble with the screws for the steps. Countersunk screws it is!