Esa grapadora pesa menos de lo que parece, pero grapa mejor que la mía.

Esa means that and esta means this.

Spanish makes a three-way distinction with demonstratives:

• esta = this
• esa = that
• aquella = that over there / that more distant one

So esa grapadora means that stapler. The choice depends on how the speaker sees the stapler in relation to themselves and the listener.

Also, esa is feminine singular because grapadora is feminine singular.

Because they both refer to grapadora, which is a feminine singular noun.

In Spanish, words that go with a noun usually have to agree with it in gender and number:

• esa grapadora
• la mía

If the noun were masculine, the forms would change:

• ese libro
• el mío

Even when grapadora is omitted in la mía, the feminine form stays because the missing noun is still understood.

Because Spanish often uses más/menos de lo que + verb when comparing an amount or degree with a whole clause.

Here the idea is:

• it weighs less
• than what it seems / than it appears to weigh

So de lo que is the natural structure.

This pattern is very common:

• Gasta más de lo que gana = He spends more than he earns.
• Es menos difícil de lo que parece = It’s less difficult than it seems.

Using menos que parece here would sound incomplete or unnatural to most speakers.

Here lo que refers to an abstract idea: what or the amount that.

In this sentence, lo que parece is roughly:

• what it seems
• or more naturally in English, than it seems

The lo is not masculine. It is a neuter article, used for general or abstract things rather than a specific noun.

So de lo que parece is basically than what it seems or than it appears to be.

Yes, you can think of an idea like pesar as being understood.

So:

• pesa menos de lo que parece

really means something like:

• it weighs less than it seems to weigh

Spanish, like English, often leaves that repeated idea unstated because it is already obvious from context.

Because grapa is the third-person singular present form of the verb grapar.

• grapar = to staple
• grapa = it staples / he staples / she staples

So in the sentence, grapa mejor means it staples better.

This can surprise learners because grapa is also a noun meaning staple. But here it is clearly a verb because of the structure:

• pero grapa mejor que la mía

In Spain, grapar is a normal verb for using a stapler.

Because mejor is a comparative, and comparatives normally take que:

• mejor que = better than
• peor que = worse than
• más que = more than
• menos que = less than

So:

• grapa mejor que la mía = it staples better than mine

You would not use de after mejor in this kind of comparison.

Because when Spanish uses a possessive pronoun on its own, it normally takes the definite article:

• el mío
• la mía
• los míos
• las mías

So la mía means mine, with grapadora understood.

Compare:

• mi grapadora = my stapler
• la mía = mine

The article is required in standard Spanish in a sentence like this.

Because Spanish often leaves out subject pronouns and repeated subjects when they are already clear.

The subject of grapa is still esa grapadora from the first part of the sentence:

• Esa grapadora pesa menos de lo que parece, pero grapa mejor que la mía.

English usually repeats it, but Spanish does not need to. Repeating the subject would sound more emphatic than necessary.

Because pero simply means but and connects two contrasting ideas.

That is exactly what is happening here:

• it weighs less than it seems,
• but it staples better than mine.

Sino is different. It is used after a negation to correct or replace something:

• No es roja, sino azul = It isn’t red, but rather blue.

Since the first clause here is not negative, pero is the correct conjunction.

Yes, grapadora is very common in Spain for stapler.

In other Spanish-speaking countries, you may also hear forms like:

• engrapadora
• sometimes other regional terms

So for a learner focusing on Spanish from Spain, grapadora is a very natural choice.