I need a manual for a Mercury M-120-1 industrial sewing machine

Nothing available. This is all there is, plus it is South African and we are in North America. Industrial machines like this one is very simple.

Harrison Sewing - Ahmeds Textiles

ahmeds.co.za https://ahmeds.co.za > collections > harrison-sewing Harrison Sewing. 1 product. Sort. Featured; Best selling; Alphabetically, A-Z ... Harrison Industrial Lockstitch Machine - GC8700. from R 9,500 from R 9,500.00 ...

Their original field appears to be industrial lathes.

https://www.google.com/search?q=harrison+sewing+machine+manual

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No free ones, but they are low cost anyway.

https://www.sewingonline.co.uk/toyota-industrial-manuals.html

and

https://www.sewingwishlist.com/toyota-industrial-manuals.html

Parts

https://www.sewingmachinesaustralia.com.au/shop/buy-spare-parts/toyota/toyota-ls2-ad158

..

Reliable - Single Needle Sewing Machine

reliablecorporation.com > collections > single-needle

Since 1955, Reliable machines have been the benchmark in sewing innovation and craftsmanship, including the SewQuiet servomotor, the industry leader.

Dejavu House INDUSTRIAL SEWING STANDARD NEEDLE ...

www.amazon.ca > Dejavu-House-INDUSTRIAL-Replac...

Dejavu House INDUSTRIAL SEWING STANDARD NEEDLE Replacement for ... LS2-1130 RELIABLE MSK-8800, MSK-8550M, MSK-8870M: Amazon.ca: Home ...

Reliable Single Needle, Drop Feed Sewing Machine, MSK ...

www.sewingmachinesplus.com > sewing-machine-relia...

Disclaimer: Due to the weight of the table with motor, there might be some minor marring or scratches due to shipping. This is normal when shipping industrial ...

KASINGS Industrial Needle Plate Replacement ... - Amazon.com

www.amazon.com > NewPowerGear-Industrial-Replace...

Amazon.com: KASINGS Industrial Needle Plate Replacement For MITSUBISHI LS2-190, LS2-1130 RELIABLE MSK-8800, MSK-8550M, MSK-8870M: Home ...

RELIABLE MSK-8900M INSTRUCTION MANUAL Pdf ...

www.manualslib.com > ... > MSK-8900M

Reliable single needle walking foot sewing machinee specification sheet (1 page) ... Reliable industrial blindstitch machine instruction manual (34 pages).

industrial sewing machine roller foot single-needle high shank ...

www.aliexpress.com > ... > Sewing Tools & Accessory

Reliable : MSK-8800, MSK-8550M, MSK-8870M Rex : RX8500 Singer : 31-15, 95, 96, 120U, 121C, 121D, 188K, 191D, 195K, 196K, 241, 251, 281, 366K, 400W, ... Rating: 5 · ‎1 review · ‎US$0.99 · ‎In stock

Try manualsonline.com or the manufacturer.

Perhaps a manual would be helpful:

File JUKI DDL 8300N Instruction Manual pdf

You should probably contact the manufacturer with questions. Hopefully, you did some thorough research before purchasing this machine. From the info I found, it appears to be a straight stitch only machine. I don't know anything about this machine, but I would be hesitant to purchase a straight stitch machine for sewing swimwear. Usually, swimwear needs a stretch stitch or zig-zag capability. Just my thoughts...

Amazon com Juki DDL 8700 Industrial Straight Stitch Sewing Machine Arts...

Juki DDL 8300N Industrial Single Needle Lockstitch Sewing Machine with...

JUKI DDL 8300N Straight Stitch Industrial Sewing Machine With Table Lamp...

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any sewing rade shop will have an assortment of needles
they will be able to advise you on the correct needle to use for different materials that can be sewn
there is a site on the net that explains the needle sizing and uses
go google and type in--- needles for industrial sewing machines ---
pick the information for singer or read what is pertinent to singer

Go to this webpage to download one, it is free but you must register.
http://www.sewingmachinemanuals.com/pfaff-138

my thread deeps bursting, tension is normal. what to do?

check with sewvacdoctor.com