"Instant" welding script issue, throws an error on Line 58?

Generic For Loops

There is a way you can avoid this problem entirely, by switching from numeric for loops to generic for loops. A numeric for loops would be the most common type of for loop, found in almost every language.

Ex:

for iter = start, finish, increment do
    ...
end

However, lua has a more intuitive way to handle your current situation, a generic for loop, which can be formatted as such:

for index, value in pairs(table) do
    ...
end

Using the generic for loop, you can easily shorten the process of iterating through tables from

for i = 1, #table do
    if table[i] == "something" then
        ...
    end
end

to

for i,v in pairs(table) do
    if v == "something" then
        ...
    end
end

Application

This won't just shorten your script, it solve your current problem, which all relate to the length operator and the declaration of for loops.

Note: you could use the spawn() function instead of resuming a created coroutine

local function InstantWeld()
    CurrentWelds = {} -- Empty the table
    GetObjects(Handle)

    spawn(function()
        wait()
        for a_,Val1 in pairs(Handle:GetChildren()) do
            local v1 = Parts
            for _,Val2 in pairs(v1) do
                if d:IsA("Weld") then
                    local Break = false
                    for _, Val3  in pairs(CurrentWelds) do
                        if Val2 == Val3 then
                            Break = true
                        end
                    end
                    if not Break then
                        Val2:Destroy()
                    end
                end
            end
        end
    end))
end

Tool.Equipped:connect(function()
    InstantWeld()
end)

Tool.Unequipped:connect(function()
    InstantWeld()
end)
InstantWeld()

Note: I am not fully aware of what you are trying to accomplish, so I just ended up modifying your original script :p

Original Errors

1: Declaring a for loops with local instead of for\

 local v2 = 1, #v1 do

Fixed Version :

for v2 = 1, #v1 do

end

2: using a table instead of a number as the finish point of a numeric for loop

for Parts = 1, Handle:GetChildren() do

FixedVersion`

for Parts = 1, #Handle:GetChildren() do

References

generic for loops

Hopefully this helped with your problem!

if there is anything i missed, just leave a comment

I think the issue, based on the error, is this line:

for Parts = 1, Handle:GetChildren() do

When you call Handle: GetChildren() you are asking for a Table, not a number, so you need to place a Hashtag in front of it like:

for Parts = 1, #(Handle:GetChildren()) do

I'm not sure if you need the extra parentheses, if you dont, remove them, but just in case this should work:

local handle = Handle:GetChildren()
for Parts = 1, #handle do

Please note this is simply based on the amount of the script I have access to, so I can't tell if this is the true cause of the error (there is no line 58 in the Question)

EDIT: I just looked at your other attempt, which functioned similar to this, but I can't tell why you tried to get the # of #Part, since #Part was already a number to begin with

Regarding Comment #1

Try this, since you already have a # from the handle, a second iteration is not required

local handle = Handle:GetChildren()
for i = 1, #handle do
    if handle[i]:IsA("Weld") then 
        local Break = false
        for v3 = 1, #CurrentWelds do
            if handle[i] == CurrentWelds[v3] then
                Break = true
            end
        end
        if not Break then
            handle[i]:Destroy()
        end
    end 
end