On 11/3/2009,Doug Schimke wrote:
"The dipstick did not have an extension on the block. Whilst at VB recently I picked one up, only to find that it would not thread into the block".

Is it wrong thread on the tube, or no thread in the block? The only blocks I have ever seen with no thread there would be for some other application with dipstick in some other location, like a Magnette for instance. If you have a non-MGA block, you may have to drill and tap the hole.

I just unscrewed the one from my spare engine. I had never removed one before but it surprised me and came out with finger force only. The thread is 3/8-28-UNEF. I don't have any Extra Fine taps or dies, and no matching nut to try on it, but it measures exactly 0.375" major diameter and meshes perfectly with a 1/4-28-UNF bolt or thread gauge.

Addendum Sep 16, 2023:
This thread size came into question again when someone received a new dipstick tube from Moss Motors that did not fit into the thread on the engine block. Since the old part screws right it only finger tight, and the new one does not fit, we suspect the new one is a faulty part with incorrect thread, still being investigated.

If it is 3/8 Unified thread, then it would be 3/8-28 UN, not 3/8-28-UNEF (as 3/8-UNEF is 32 threads per inch).

But it strikes me that most of the port threads in these Austin B-series engines are BSPP standard threads (British Standard Pipe Parallel). If this one is also BSPP thread, then it would be 1/8-BSPP thread, which is exactly 28 threads per inch. But it is also 0.383-inch major diameter and 55-degree thread angle Whitworth standard thread. Slightly larger then 3/8-inch, and difficult to tell the 55-degree thread angle by eye sight.

I will put this tech article on probation pending further investigation. Meanwhile, if anyone has a definitive answer to this question, please do tell. Click on my name below for my email link. -- Barney