Thread size for external speakers (Icom SP35 etc.)

[N9JIG]

I have a variety of external speakers and need to know the thread size for the mounting threaded inserts on the sides. The Icom SP35 and those ubiquitous rectangular speakers from PowerWerx, Opek and others all seem to use the same size threads.

For a project I need to find out the thread size so I can order some hardware. In order to save a 45 minute each way trip to the hardware store does anyone know the thread size?

Thanks!

 

[AK9R]

See if you have other radio mounting screws in your junk drawer that fit. Then take that screw to the hardware store to match to their inventory.

My WAG would be #10 or M4. Not sure about thread pitch.

 

[JDKelley]

I don't know how to help you now (other than to say to take the speaker with you. . .) but most MRO mailorders will offer something called a "thread detective" or something ismilar. It's a series of threaded bungs - one end external thread, one end internal - on a cable and all stamped with the size.

My hardware store is 10 minutes away, and that thing sees extensive use! Something like this - https://www.amazon.com/gp/aw/d/B0CB...d_r=b550a7de-f629-4886-afc7-a0a083d89eff&th=1 - you'll find that there is a "standard size" version (runs 1/4"ish to 1/2-3/4"ish/M6-M20) and a "small thread" size (under 1/4" or under 6mm.) The "standard" size is usually a combination, and the small sizes are dedicated SAE or ISO.

Both standard and coarse threads are identified, simply be screwing the bung into the hole you want to check, or the unknown screw into a bung it finally fits properly in (2-3 full turns, either way.)

Let's just say I work on a LOT of odd projects, they paid for themselves in fuel saved for me within two months. . .

 

[K4EET]

Hi @N9JIG. I don’t know the screw/bolt size you need but I wanted to suggest investing in one of these if you find yourself in that situation very often. Mine has been a real lifesaver multiple times. I can no longer drive so I mail order or have Home Depot / Lowe’s deliver my needs without guessing at the nuts and bolts sizes.

https://www.amazon.com/Checker-Standard-Identifier-Detachable-Especially/dp/B0FH4SG3YP/

 

[K4EET]

I don't know how to help you now (other than to say to take the speaker with you. . .) but most MRO mailorders will offer something called a "thread detective" or something ismilar. It's a series of threaded bungs - one end external thread, one end internal - on a cable and all stamped with the size.

My hardware store is 10 minutes away, and that thing sees extensive use! Something like this - https://www.amazon.com/gp/aw/d/B0CBPGN54R/?_encoding=UTF8&pd_rd_plhdr=t&aaxitk=2d46072ef8d9f5ab5f573738b3eb1305&hsa_cr_id=0&qid=1771355706&sr=1-2-9e67e56a-6f64-441f-a281-df67fc737124&ref_=sbx_s_sparkle_sbtcd_asin_1_img&pd_rd_w=XZ31c&content-id=amzn1.sym.9f2b2b9e-47e9-4764-a4dc-2be2f6fca36d:amzn1.sym.9f2b2b9e-47e9-4764-a4dc-2be2f6fca36d&pf_rd_p=9f2b2b9e-47e9-4764-a4dc-2be2f6fca36d&pf_rd_r=3XVT7FV38FGQ4NK2MSX1&pd_rd_wg=XDOX5&pd_rd_r=b550a7de-f629-4886-afc7-a0a083d89eff&th=1 - you'll find that there is a "standard size" version (runs 1/4"ish to 1/2-3/4"ish/M6-M20) and a "small thread" size (under 1/4" or under 6mm.) The "standard" size is usually a combination, and the small sizes are dedicated SAE or ISO.

Both standard and coarse threads are identified, simply be screwing the bung into the hole you want to check, or the unknown screw into a bung it finally fits properly in (2-3 full turns, either way.)

Let's just say I work on a LOT of odd projects, they paid for themselves in fuel saved for me within two months. . .

Beat me by seconds…

 

[JDKelley]

See if you have other radio mounting screws in your junk drawer that fit. Then take that screw to the hardware store to match to their inventory.

My WAG would be #10 or M4. Not sure about thread pitch.

#10 could go either way - #10-24 or #10-32. M4 would most likely be M4-0.7 (coarse.) M4-0.5 (fine) is possible, but unlikely.

 

[JDKelley]

Beat me by seconds…

Gotcha!

The only real difference between your idea and mine is that mine are permanently stuck together, so one doesn't get lost (which will invariably be the one you need. . .) And I just hang them on a hook on the side of my toolbox, so I can get at them easily.

 

[N9JIG]

I ordered the thread checker suggested by JDKelley for two reasons. First it will arrive overnight (supposedly) and second I can see occasions where it will be handy to use the individual pieces not chained together.

I could go to the hardware store and use their checker but that is 45 minutes each way and I know I am going to have to order the parts based on the size the thread is determined to be.

If this idea I have formulating in my head works I will be posting pictures next week... The gears are turning!

 

[ramal121]

Can confirm a SP35 uses M4.0 P0.7 screws. Same as the radio sfrews for Kenwood, Most Icoms etc.

 

[AK9R]

@N9JIG once you find the screw size you need, you can avoid the limited selection at your hardware store and visit McMaster-Carr online. They will have the exact thread, length, and head type that you want. Granted, you may have to buy a box of 100, but it will satisfy your OCD.

 

[KJ4DHF]

The Motorola RSN4003A speaker uses m4-0.7

 

[N9JIG]

Well, I figured out another way around it and was able to complete the little project with stuff at hand. I looked thru my parts drawers and found a few 2-inch machine screws with the correct thread (whatever it is...). I then cut these in half and cut the heads off. I did this for 6 screws, making 12 studs. All but one worked fine, one must have shifted during cutting and the thread was messed up.

I will keep the thread sizer for future use, it will come in handy for sure! I might even take a day or so and sort all my accumulated nuts, bolts and machine screws by size if I really get bored some day when it is too hot to go outside.

Pictures of the finished project are at Winter 2026 N9JIG Build

 

[N9JIG]

Can confirm a SP35 uses M4.0 P0.7 screws. Same as the radio sfrews for Kenwood, Most Icoms etc.

Great, thanks!

 

[JDKelley]

@N9JIG once you find the screw size you need, you can avoid the limited selection at your hardware store and visit McMaster-Carr online. They will have the exact thread, length, and head type that you want. Granted, you may have to buy a box of 100, but it will satisfy your OCD.

Amazon absorbed a niftly little MRO I used extensively in maintenance called Small Parts, Inc - and that's exactly what they did. I think you can get screws down to M1.6 or #000 on Amazon without any trouble, and within a couple days' delivery timeframe. They also did odd materials - I could get screws from them in Nylon (not very odd) or glass (for chemical resistance.) I don't know if Amazon does their whole line - some of the stuff they stocked before was pretty niche market.

McMaster can get you nearly anything (and it doesn't hurt to ask for a catalogue when ordering - worst that can happen is they say No. This is the time of year to do it!) but they're proud of their stuff, and it's hit-or-miss on rapid delivery (they don't ship like Amazon does, and you don't know where in the country it's coming from. I could order here near San Francisco, and have it come from LA, Reno, Seattle, or Pennsylvania. . . Or all four.) The minimum quantity/minimum order value factor also applies. You can get nearly anything from them, but I consider them as "weapon of last resort."

Another useful little source for small fasteners is a modelmaker's house called Micro-Mark - they cater to submini (I had to order #2 screws to fix a minitature brass sextant for my mom, and #2 screws were on the large end of their charts!) markets, but they also have miniature machine tools (which I might have gotten if I didn't already have a set from Sherline. However, the Sherlines I did get are a bit more capable, at 7x17 for the lathe and an 8-axis mill, both of which can be later converted to CNC, once I get my head around it a little better. I learned to make chips the old-fashioned way. . .) Micro-Mark has smaller order minima. (When I ordered those #2 screws, they were all I had to order - I just had to get 20 of them to a packet. So, I've got more for later. I work on small stuff all the time, so they fit right into my spares kits. . .)

MSC Direct is another MRO house, good for parts, a bit better in the ordering and shipping than McMaster (but light on the "exotic/oddball" stuff. If MSC doesn't have it, go to McMaster. If McMaster doesn't have it, make it yourself or redesign it to use a standard part.)

www.micromark.com
www.sherline.com
www.mcmaster.com
www.mscdirect.com