Can someone who is not far from a D4 6U or 7U measure up the tilt adjuster for a 4A blade for me? I need to make a tool to fit over mine and I'm not near enough to measure (3hrs away). I want the overall diameter, and depth/length of the adjuster head. Would be great if I knew the distance of the drive holes from the top of the head too. 

Paul. 

we replaced the original bolts on ours with high tensile allen head bolts we can tighten them with a large allen key or a hex bit and breaker bar the originals just took a lenght of 5/8 round bar.
they were siezed solid so i just cut em off.
when you get yours apart or replace them put some nickle anti-sieze on the threads so they undo next time and actually they tighten better too.

To answer your question and not offering an alternative:

Bolt is 1 1/4" 12 tpi (slo), 2 7/8" long. The head is 2" in diameter and 1 3/8" thick/; tall. Adjustment/ tightening holes are 3/4" diameter, and are 1/4" up from shoulder.Backing plate is 4" long and bent in an arc to match the blade frame - only about 1/16" over 4 inches.

 

Very much appreciated willwingo! Thankyou.

I'm hopeful I can still free these up without ruining them.

Paul.

Trainzkid88 - if I can't get these out intact I'll do as you've done. I've been using silver anti-seize on everything. I don't know what materials that is suitable for though (have just been assuming some is better than none).

Paul.

Get the backer red hot. If you lose the threads, you can use a longer 1 1/4" slo thread grade 8 bolt and nut. May have to enlarge the hole so the threads will past.

Most often the nut gets welded to the backer - then you will not need a wrench to tighten - just the bar. This bolt is not under a great deal of pressure - just keep it tight

there's 3 types of anti-seize nickel, copper or calcium based(food grade)
there suitable on virtually all metals its more operating temp and chemicals that make a difference. you can also use plain old bearing grease. graphite grease is good too

be careful using heat you can make it worse. if its available in the states get a product called penetrene its a very good penertrant. give it a liberal spray and let it soak.

we had to cut the original nut so i just got 3 pieces of 1/4 flat bar gave em a slight curve in the press spotted em together, drilled it to suit the bolts and spotted the nut on

Here is an update on this topic. I made a tool to give me good purchase on the adjuster head. Unfortunately it wasn't close. Whoever (Steelweld?) made the Australian 4A blades used different specs. The adjuster nut diameter on this one is 2 1/4". Holes are closer to 13/16", and other dimensions are a little different.
     

I did get them freed up with heat and 'kroil'. Now that they're free, I'm tossing up whether to bother remaking the tool or just use a podger.
 

Paul.