Assuming that the nut you are looking for is for the twin spring forks of 2.3/4 or 4 hp or even some later models then the thread size is 3/8" x 28 tpi not 25 tpi. In my restorations I have always re-manufactured these as invariably they are rusty and worn where they act as a pivot for the spring eyes. As a result I currently have plenty of these nuts in my scrap box. If you get no response to your request in Australia let me know and I will post you a couple. Chris.