were to place the metallic map in 3ds max standard material map slots

thats all good i jsut leave note in my models. to say im always on hand to enable the best possible render to support em .. cheers

There's no absolutely perfect way to set up your maps and everything in OBJ so that they open the same way in every software. It's not going to happen no matter what. FBX format offers a decent workaround to this. With FBX, just like .blend files in Blender, you can "pack" your maps into the FBX file itself. Then when the person opens the FBX in a software package, the packed textures will unpack automatically in the intended spots. It's still not perfect, but far more convenient than OBJ. This is why it's always good to offer more than just one type of exchange format, and also include a native file format if possible so that clients can transfer the asset to where they need it in their own pipelines themselves. Some clients may have a .js script or something custom in their pipelines that was purposely created to move assets from maya, 3dsmax, or whatever into the game engine. The best bet is to offer a native file format, an FBX with packed textures (if possible), and then an OBJ configured to the best of your knowledge. Then also include a download for your texture files in a zip or whatever. At least if the Diffuse (albedo) and normal maps load with OBJ, it's very easy for anyone to just customize with the other maps you have included.

if ur bake the map tho could casue other issue with games engines im geesiing blender unreal engine unity dont all w ork in the same way

...and the Roughness map in the Glossines slot for *.obj.

That will transport the paths in the .mtl for OBJ, but the clients will still need to make the changes manually. A roughness map inverted with the bitmap settings will not export as an inverted map for glossiness unless it's procedural and you bake the result to a new map.

PS: It seems if you have acess to the Direct X shader in 3dsmax, you can use that to export PBR to FBX as well. Again, this isn't going to apply to OBJ.

i did place them in standard material map slots (roughness to glossiness with invert)

the ony reason im dooing this is to try help people when they buy the models to load the shader in chosen package

That's the limitation of OBJ to begin with. It does not natively support PBR in the .mtl definition file, so you can do a few tricks to fake it like plugging a normal map directly into the bump channel of a standard shader so that the exported path for the bump leads to the normal map, but there's always going to be some manual work adjusting maps with OBJ files. OBJ is the most widely accepted file format, but it's a very old format and is quickly becoming obsolete. OBJ has the potential to become much more robust, but it's up to the software designers to incorporate these features into the OBJ loader scripts. You could do it by hand by editing the OBJ and MTL files in a text editor, but that still doesn't change how it will import into the software if the features just aren't supported in the loader. Hope I'm making sense here.

3ds Max standard shader trying pack pbr maps my into fbx format . I am unable to locate metalness slot in the standard shader . ( i didnt think there was metal area in this standard material.....(base color placed diffuse), roughness placed glossiness) ,mmmm,,,,, metalness ?unable to locate the slot? pleae see image https://ibb.co/fdMTRKs