Ohne Maßband ist es schwer, den Abstand zwischen den Löchern richtig zu messen.

Both are possible, but ohne Maßband sounds more general: without a measuring tape / without measuring tape.

German often leaves out the article when talking about something in a general, non-specific way. So:

• ohne Maßband = without a measuring tape, in general
• ohne ein Maßband = without a specific measuring tape

In this sentence, the article-less version sounds very natural.

Ohne always takes the accusative.

So in ohne Maßband, Maßband is in the accusative. You cannot see a form change here because das Maßband is the same in nominative and accusative:

• nominative: das Maßband
• accusative: das Maßband

If the noun were masculine, the change would be more visible.

Because Abstand is the direct object of messen.

The verb messen takes an accusative object: you measure something.
Here, what is being measured is the distance, so German uses the accusative:

• nominative: der Abstand
• accusative: den Abstand

That is why the sentence has den Abstand.

Because zwischen is a two-way preposition. It can take:

• dative for a location/static position
• accusative for direction/movement toward a place

Here the sentence is talking about the distance located between the holes, not movement from one place to another. So German uses the dative:

• zwischen den Löchern = between the holes

If it were about movement into a position between something, accusative could appear, but not here.

Because it is dative plural.

The plural of das Loch is die Löcher. In the dative plural, German often adds -n if the plural form does not already end in -n or -s:

• nominative plural: die Löcher
• dative plural: den Löchern

So zwischen den Löchern is exactly what we expect.

This es is a dummy subject or placeholder subject.

German often uses es in expressions like:

• Es ist schwer, ...
• Es ist wichtig, ...
• Es ist gut, ...

It does not refer to a specific thing. It just fills the subject position in the sentence. In English, we do the same:

• It is hard to measure...

So the es here works very much like English it in it is hard.

Because German main clauses follow the V2 rule: the finite verb must be in the second position.

The first position can be taken by many kinds of elements, not just the subject. Here, the sentence begins with the prepositional phrase:

• Ohne Maßband = first position

So the finite verb comes next:

• ist = second position

Then the subject-like es comes after that:

• Ohne Maßband ist es schwer, ...

This is completely normal German word order.

Because German often uses an infinitive clause with zu after adjectives like schwer.

The basic pattern is:

• Es ist schwer, etwas zu tun.
• It is hard to do something.

So here:

• Es ist schwer, den Abstand zwischen den Löchern richtig zu messen.

The whole part after the comma explains what is hard. German places that zu + infinitive structure at the end of the clause.

Here richtig means something like:

• correctly
• properly
• accurately

It is an adverb modifying messen. So the idea is not just to measure the distance, but to measure it correctly/accurately.

In context, richtig is very natural because measuring can be done in a wrong or inaccurate way.

Because there is only one distance being talked about: the distance between the two holes.

So German uses the singular:

• der Abstand zwischen den Löchern

English does the same:

• the distance between the holes

Even though there are two holes, the distance itself is one thing.

Das Maßband means measuring tape or tape measure, depending on context.

It is made from:

• Maß = measure / measurement
• Band = band / strip / tape

So literally it is something like measure-tape.

In everyday use, Maßband is a very common word for a flexible tape used for measuring.

The letter ß is called Eszett or scharfes S.

It is pronounced like ss in English mass. So:

• Maßband is pronounced roughly like mass-bahnt (very approximately)

It does not sound like a z.

In modern German spelling, ß often appears after a long vowel or diphthong, while ss appears after a short vowel. For learners, the most important point here is simply:

• Maßband and Massband would not be standardly spelled the same way
• ß sounds like ss

No, the comma is correct and expected here.

German normally uses a comma before an extended zu-infinitive clause like this one:

• Es ist schwer, den Abstand zwischen den Löchern richtig zu messen.

The comma separates the main clause:

• Ohne Maßband ist es schwer

from the infinitive clause:

• den Abstand zwischen den Löchern richtig zu messen

So the comma is an important part of standard written German here.