zhè shì wǒ de tóukuī.

I

Breakdown of zhè shì wǒ de tóukuī.

• 是shì: to be
• 这zhè: this
• 的de: possessive particle

Questions & Answers about zhè shì wǒ de tóukuī.

What does each part of 这　是　我　的　头盔 mean?

Word by word:

• 这 = this
• 是 = to be / is / am / are
• 我 = I / me
• 的 = a particle that shows possession, similar to 's or of
• 头盔 = helmet

So the structure is:

• 这
  • 是
    • 我的头盔
• This
  • is
    • my helmet

Why is 这 used by itself here? Why not 这个?

In this sentence, 这 is a pronoun, meaning this by itself.

• 这是我的头盔。 = This is my helmet.

If you wanted to say this helmet, where this directly modifies the noun, you would usually need a measure word:

• 这个头盔 = this helmet

So:

• 这 = this as a standalone thing
• 这个头盔 = this helmet

That is why 这 alone is correct in 这是我的头盔。