Peening tool, little secret..

Hi all!

I've bought a closure that came with nails :

The tool needed for the installation is called "peening tool", very hard to find in the leather craft sphere and expensive (130$ at Rm leather).

After research and diggings, i've found that this tool is used in two spheres essentially : - Jewelry / Watches making - Eyewear (glasses making).

In jewelry, the tool is called "Perloir", very cheap (about 2$) with hard steel, high gloss and polished calotte, but the largest diameter is 1,35mm, which is not what we need.. https://www.vallorbe.com/file.cfm?cmsfile=&contentid=5112

In Eyewear, the tool is called "Bouterolle" (this term exists in jewelry but for a different tool), prices vary from 2$ to 15 :

https://www.otelo.fr/bouterolles-rivets/64111005/SF-ID-00101912/ref-25871.html

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https://www.materiel-optique.fr/pointeaux/614-assortiment-outils-de-choc-sur-socle-en-bois.html

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https://www.essishop.fr/bouterolle-bruni-d-2mm The last one looks like the one used by Hermès at 25mn in this video :

Have some of you tried these tools? What would be the best size between 2mm and and 3mm? And last but not least, how do you manage to protect the front piece of the lock while peening the nails in the back? I thought about doing it on a mattress..

Should i flatten them? They will be under the lining. Any tips would be great as this subject being not very documented.. Thank you all!