What thread size is this? Laser 301/303 front end.

[Marco Polo]

I'm trying to identify the size of this thread on the laser 301/301 host. It's the silver thread in the picture, the one between the black anodizing and the brass section. The stock front end screws onto this thread and focusing mechanism uses it as well. Here is the picture:

Btw, haven't made a thread for it yet, but there's how I finally replaced the scratched lenses on my green 301's. The inner threads on the brass part are M11x0.5, so an AixiZ module screws in. The lens is 1-element, AR coated, and came from my dead LaserBTB's 3-element lens. (Both the meniscus lens and the doublet from common 3E lenses work too0.) The beam clarity and divergence are much better than new, plus I think the laser looks pretty cool. Very pleased with how it turned out.

But as to that thread. I'm not 100% on it, but I think it's M19x0.75mm.

But it could also be M19x0.7mm, which is apparently used for camera lenses (?) in some fashion.

For all I know it could be an M18 or M20 thread.

Less likely, it could be non-metric, e.g. 3/4" 36 tpi. (I've seen this on some of these lasers - a few of my 301's have a weird lens holder which is probably 3/8" 48tpi, rather than metric. It won't fit M9 or M10.

Tried looking at parts online but that didn't really help, as there is no good way to compare them to anything or otherwise confirm that it's the correct part. I need to visit the camera shop tomorrow to pick up some clean lens cloths, so if nobody can identify it by then I'll see if the shop can and report back if I find out. Really appreciate it if anyone knows what it is, or has a metric thread gauge and wouldn't mind checking. Thanks!!!

 

[crazyspaz]

No definite way to tell without measuring distance between threads. pretty hard to eyeball threads, although maybe someone on here knows the threads used on those specific hosts. There are many ebay sellers that sell blank hosts of the exact type, maybe ask one what the threads are? They are chinese sellers, so not guaranteed to be the manufacturers, but its worth a shot, since they could get in contact (most likely) with the manufacturer.

 

[Marco Polo]

Well, no, you can't eyeball it, but the host is common enough, maybe somebody who has one happens to have a metric thread gauge too, machinist types, maybe. The thread pitch is finer than 1.0mm, that much I can tell but impossible to tell difference between 0.7 and 0.75. If indeed there is a meaningful difference.

I'm really hoping it's M19x0.7 because that is apparently close enough to 3/4" 36 tpi for most things.

Mainly want this thread size so I can find or make a retaining ring that would keep the heatsink in place. This would eliminate the need for a tight press fit; I have my doubts about the machining tolerances on these hosts and wouldn't surprise me if a snug fit on one host is a loose fit on another. A retaining ring or nut would address that.

The last resort would be to make a retaining ring out of a stock front end. Hacksaw and file to get it down to rough size, fine file and sandpaper to flatten the ends out, easy. Trying to avoid this for now since it results in the destruction of a front end, but if necessary I can make that work.

 

[Marco Polo]

Well, I struck out at the camera shop. At least, pretty sure. The owner wasn't in, so I left my contact info. Maybe he will know something.

I did confirm that the thread I'm looking for is 0.75mm pitch. The internal (female) thread diameter was measured with a Starrett caliper and it came to 19.5mm. The threads are not the best quality; if these were sharp threads the reading would have been much closer to 19mm. This would correspond to the minor diameter on an external (male) thread, suggesting that the major diameter is 20mm.

Thus, I believe the thread size I'm looking for is M20x0.75mm, based on the caliper reading and visual comparison of the thread pitch to a 0.75 metric tap. I hope so, because the even-numbered M-thread parts seem to be more common than odd-numbered ones. The extra-fine pitch still makes it a PITA though.