There are some gaps in my understanding of this part. First - what to call them. I hear them referred to as hood clips, hood clamps, hood catches, etc. Add to that the Australian variations where we substitute "bonnet" for "hood". I'm already confused, and we haven't even started talking about the changes over the years yet! First question - what did Ford call them?
Aside from minor variations which I attribute to different dies or possibly manufacturers, I've noticed 6 distinct styles. Here they are:
Looking from left to right, Style 1 is forged - 1909-10. Style 2 is forged - 1911-1916 (?). Style 3 is a 2 piece assembly with a forged ring - 1916-17 (?). Style 4 is pressed, 1918-? (?). Style 5 is pressed - ?-1925. Style 6 1926-27.
Here's a different perspective on style 5 and 6 showing the difference in the thickness at the top of the ring:
As you can see from the question marks my dates are guesses. Any input welcomed.
There was this study in 2013: http://www.mtfca.com/discus/messages/331880/342742.html
As I presume you have found these in Australia I think possibly the Canadian factor comes into play, The Canadian Fords were a law unto themselves, there is also the possibility that as the Australian Fords were assembled after WW1 with local bodies some body builders could have sourced the "clips, clamps, catches" locally.
In addition to the link above, see pages 527-528 in the encyclopedia where Trent Boggess gives the dates of changes.
Here is the info from the Encyclopedia:
T-1310 hood clip. The single ear design was adopted on Feb. 7, 1908 and appears to have remained substantially the same for the entire time period that it was in use. The modified the tolerances for the stem diameter slightly on Sept. 23, 1909 and again on May 9, 1910, and changed the size of the hole for the cotter pin from a #29 to a 9/64 on 8-3-10.
On June 27, 1911 the clip was redesigned. Galamb wrote “Have made two hooks for clamping Hood instead of one, making one on each side. Also changed distance between the center of ring to end of shank, from 3-3/16 to 3-1/16, also changed section of ring, from .25” diameter to elliptical section .25” to 5/32”, also note that bottom of Hooks are flat instead of round.”
The design was modified two days later on June 29, 1911 by Howard who wrote: “Changed width of Ring from .25” straight to 3/8” at top, tapering .25” at bottom, also changed width of hooks, from .25” to 5/16”, also changed thickness at top of Ring from 5.32” to 1/8”.”
No other change in the design seems to have occurred for almost five years. Then on May 18, 1916 Martin wrote “Changed name from hood clip, and material from drop forging to cast iron head, with steel stem cast in place. This obsoletes the forging.”
The next entry on the card reads “Specified for repairs only, authorized by Purdie.” This is a typo error since the release card shows that the part was used through the end of 1926. Furthermore James Purdie was in the magneto and experimental departments. Hood hooks would have been well outside of his area of responsibility.
On April 16, 1917 a T-1310 Exp. Mfg. Design was introduced. This appears to have been the stamped steel style of clip. The note reads “Production at first to be small, and gradually increased until this design of hood clip will replace the present design.”
Three months later on July 26, 1917 Gregory wrote: “Redesigned, showing the stamping design which has been manufactured experimentally, and is now adopted permanently. This part replaces T-7993 and T7596” (the stem and head casting of the previous design).
On Dec. 4, 1917 the clip was redesigned again, “bringing the drawings up to date with clips as they are being made.”
Essentially, the hooks remained the same until they were discontinued on Dec. 2, 1926 and replaced with a new design.
I have the factory drawings for the hood hold down springs and have made them for a number of years. The early repros had a problem in that someone selected a "general purpose" spring at the hardware store that was very close but had too many turns on it so that when you pull up on the hood clip you can't get it high enough to clear the lip of the hood without taking some paint off too. I decided to make them with the correct number of active turns so that the spring does not "stack" up and prevent the correct amount of travel. On the factory drawings the spring is called "Hood Clip Spring" so Ford called it a CLIP. There were 2 different springs and they differ a bunch with the later ones having way more turns and being longer. I confess I decided to make them from stainless spring steel so they wouldn't rust and you can't get paint to stick on a spring anyway since it quickly rubs off down there. The clips and springs used to start rusting as soon as the first time you pull up on the hood clip.